Logic and Critical Thinking Ch. 2 PDF

CHAPTER TWO BASIC CONCEPTS OF LOGIC Chapter Overview Logic, as field of study, may be defined as the organized body of knowledge, or science that evaluates arguments. The aim of logic is to develop a system of methods and principles that we may use as criteria for evaluating the arguments of others and as guides in constructing arguments of our own. Argument is a systematic combination of two or more statements, which are classified as a premise or premises and conclusion. A premise refers to the statement, which is claimed to provide a logical support or evidence to the main point of the argument, which h known as conclusion. A conclusion is a statement, which is claimed to follow from the alleged evidence. Depending on the logical and real ability of the premise(s) to support the conclusion, an argument can be either a good argument or a bad argument. However, unlike all kinds of passages, including those that resemble arguments, all arguments purport to prove something. Arguments can generally be divided into deductive and inductive arguments. A deductive argument is an argument in which the premises are claimed to support the conclusion in such a way that it is impossible for the premises to be true and the conclusion false. On the other hand, an inductive argument is an argument in which the premises are claimed to support the conclusion in such a way that it is improbable that the premises be true and the conclusion false. The deductiveness or inductiveness of an argument can be determined by the particular indicator word it might use, the actual strength of the inferential relationship between its component statements, and its argumentative form or structure. A deductive argument can be evaluated by its validity and soundness. Likewise, an inductive argument can be evaluated by its strength and cogency. Depending on its actually ability to successfully maintain its inferential claim, a deductive argument can be either valid or invalid. That is, if the premise(s) of a certain deductive argument actually support its conclusion in such a way that it is impossible for the premises to be true and the conclusion false, then that particular deductive argument is valid. If, however, its premise(s) actually support its conclusion in such a By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 37 way that it is possible for the premises to be true and the conclusion false, then that particular deductive argument is invalid. Similarly, an inductive argument can be either strong or weak, depending on its actually ability to successfully maintain its inferential claim. That is, if the premise(s) of a certain inductive argument actually support its conclusion in such a way that it is improbable for the premises to be true and the conclusion false, then that particular inductive argument is strong. If, however, its premise(s) actually support its conclusion in such a way that it is probable for the premises to be true and the conclusion false, then that particular inductive argument is weak. Furthermore, depending on its actually ability to successfully maintain its inferential claim as well as its factual claim, a deductive argument can be either sound or unsound. That is, if a deductive argument actually maintained its inferential claim, (i.e., if it is valid), and its factual claim, (i.e., if all of its premises are true), then that particular deductive argument will be a sound argument. However, if it fails to maintain either of its claims, it will be an unsound argument. Likewise, depending on its actually ability to successfully maintain its inferential claim as well as its factual claim, an inductive argument can be either cogent or uncogent. That is, if an inductive argument actually maintained its inferential claim, (i.e., if it is strong), and its factual claim, (i.e., if all of its premises are probably true), then that particular inductive argument will be a cogent argument. However, if it fails to maintain either of its claims, it will be an uncogent argument. In this chapter, we will discuss logic and its basic concepts, the techniques of distinguishing arguments from non-argumentative passages, and the types of arguments. Chapter Objectives: Dear learners, after the successful completion of this chapter, you will be able to:  Understand the meaning and basic concepts of logic;  Understand the meaning, components, and types of arguments; and  Recognize the major techniques of recognizing and evaluating arguments. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 38 Lesson 1: Basic Concepts of Logic: Arguments, Premises and Conclusions Lesson Overview Logic is generally be defined as a philosophical science that evaluates arguments. An argument is a systematic combination of one or more than one statements, which are claimed to provide a logical support or evidence (i.e., premise(s) to another single statement which is claimed to follow logically from the alleged evidence (i.e., conclusion). An argument can be either good or bad argument, depending on the logical ability of its premise(s) to support its conclusion. The primary aim of logic is to develop a system of methods and principles that we may use as criteria for evaluating the arguments of others and as guides in constructing arguments of our own. The study of logic increases students‘ confidence to criticize the arguments of others and advance arguments of their own. In this lesson, we will discuss the meaning and basic concepts of logic: arguments, premises, and conclusions. Lesson Objectives: After the accomplishment of this lesson, you will be able to:  Understand the meaning.  Identify the subject matter of logic.  Understand the meaning of an argument.  Identify the components of an argument.  Understand the meaning and nature of a premise.  Comprehend the meaning and nature of a conclusion.  Recognize the techniques of identifying the premises and conclusion of an argument. What is the Meaning of Logic? Activity # 1: - Dear learners, how do you define Logic? Dear learners, the word logic comes from Greek word logos, which means sentence, discourse, reason, truth and rule. Logic in its broader meaning is the science, which evaluates arguments By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 39 and the study of correct reasoning. It could be also defined as the study of methods and principles of correct reasoning or the art of correct reasoning. Logic can be defined in different ways. Here below are some definitions of logic:  Logic is a science that evaluates arguments.  Logic is the study of methods for evaluating arguments. More precisely, logic is the study of methods for evaluating whether the premises of arguments adequately support or provide a good evidence for the conclusions.  Logic is a science that helps to develop the method and principles that we may use as a criterion for evaluating the arguments of others and as a guide to construct good arguments of our own.  Logic is the attempt to codify the rules of rational thought. Logicians explore the structure of arguments that preserve truth or allow the optimal extraction of knowledge from evidence.  Logic is one of the primary tools philosophers use in their inquiries. The precision of logic helps them to cope with the subtlety of philosophical problems and the often misleading nature of conversational language. In logic, as an academic discipline, we study reasoning itself: forms of argument, general principles and particular errors, along with methods of arguing. We see lots of mistakes in reasoning in daily life and logic can help us understand what is wrong or why someone is arguing in a particular way. What is the Benefit of Studying Logic? ―Logic sharpens and refines our natural gifts to think, reason and argue.‖ (C. S. Layman) Activity # 2: - Dear learners, what do you think is the benefit of studying logic? Discuss with the student(s) beside you. We use logic in our day-to-day communications. As human beings, we all think, reason and argue; and we all are subject to the reasoning of other people. Some of us may think well, reason well and argue well, but some of us may not. The ability to think, reason and argue well might partially be a matter of natural gift. However, whatever our natural gifts, they can be refined, improved and sharpened; and the study of logic is one of the best ways to refine one‘s natural By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 40 ability to think, reason and argue. Likewise, as academicians, our arguments must be logical and acceptable; and the tool to do so is provided by logic. In general, the following are some of the major benefits that we can gain from the study of logic:  It helps us to develop the skill needed to construct sound (good) and fallacy-free arguments of one‘s own and to evaluate the arguments of others;  It provides a fundamental defense against the prejudiced and uncivilized attitudes that threaten the foundation of a civilized and democratic society;  It helps us to distinguish good arguments from bad arguments;  It helps us to understand and identify the common logical errors in reasoning;  It helps us to understand and identify the common confusions that often happen due to misuse of language;  It enables us to disclose ill-conceived policies in the political sphere, to be careful of disguises, and to distinguish the rational from irrational and the sane from the insane and so on. The aim of logic, hence, is to develop the system of methods and principles that we may use as criteria for evaluating the arguments of others and as guides in constructing the arguments of our own in our day-to-day lives. Thus, by studying logic, we are able to increase our confidence when we criticize the arguments of others and when we advance arguments of our own. In fact, one of the goals of logic is to produce individuals who are critical, rational and reasonable both in the sphere of public and private life. However, to be full beneficial of the worth which logic provides, one must thoroughly and carefully understand the basic concepts of the subject and be able to apply them in the actual situations. What is an Argument? Activity # 3: - Dear learners, what do you think is an argument? What comes to your mind when you think of an argument? Discuss with the student(s) beside you. Dear learners, the word ‗argument‘ may not be a new word to all of us. For all of us encounter arguments in our day-to-day experience. We read them in books and newspapers, hear them on By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 41 television, and formulate them when communicating with friends and associates. If you look back at the above different definitions of logic and characterizations, you will certainly find one thing in common: argument. Moreover, we have said that of the various benefits of studying logic, identifying, analyzing and evaluating arguments is the most important one. It follows that argument the primary subject matter of logic. What is an argument then? Argument is a technical term and the chief concern of logic. Argument might have defined and described in different ways. When we define an arguments from logical point of view, it is a group of statements, one or more of which (the premise) are claimed to provide support for, or reason to believe, one of the other, the (conclusion). As is apparent from the above definition, the term ‗‗argument‘‘ has a very specific meaning in logic. It does not mean, for example, a mere verbal fight, as one might have with one‘s parent, spouse, or friend. Let us examine the features of this definition in detail. First, an argument is a group of statements. That is, the first requirement for a passage to be qualified as an argument is to combine two or more statements. But, what is a statement? A statement is a declarative sentence that has a truth-value of either true or false. That is, statement is a sentence that has truth-value. Hence, truth and falsity are the two possible truth- values of a statement. A statement is typically a declarative sentence. In other words, statement is a type of sentence that could stand as a declarative sentence. Look the following examples: a) Dr. Abiy Ahmed the current Prime Minister of Ethiopia. b) Mekelle is the capital city of Tigray Region. c) Ethiopia was colonized by Germany. Statement (a) and (b) are true, because they describe things as they are, or assert what really is the case. Hence, „Truth‟ is their truth-value. Whereas statement (c) is false because it asserts what is not, and „Falsity‟ its truth-value. N.B: Logicians used proposition and statement interchangeably. However, in strict (technical) sense, proposition is the meaning or information content of a statement. In this chapter, the term statement is used to refer premises and a conclusion. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 42 However, there are sentences that are not statements, and hence should be used to construct an argument. Examples: a) Would you close the window? (Question) b) Let us study together. (Proposal) c) Right on! (Exclamation) d) I suggest that you read philosophy texts. (Suggestion) e) Give me your ID Card, Now! (Command) In fact, sentence is a group of words or phrases that enables us to express ideas or thought meaningfully. However, unlike statements, none of the above sentences can be either true or false. Hence, none of them can be classified as statement. As a result, none of them can make up an argument. Second, the statements that make up an argument are divided into premise(s) and conclusion. That means, the mere fact that a passage contains two or more statements cannot guarantee the existence of an argument. Hence, an argument is a group statement, which contains at least one premise and one and only one conclusion. This definition makes it clear that an argument may contain more than one premise but only one conclusion. Activity # 4: - Dear learners, if argument is a combination of premise(s) and conclusion, what do you think are premise and conclusion? Argument always attempts to justify a claim. The claim that the statement attempts to justify is known as a conclusion of an argument; and the statement or statements that supposedly justify the claim is/are known as the premises of the argument. Therefore, a premise is a statement that set forth the reason or evidence, which is given for accepting the conclusion of an argument. It is claimed evidence; and a conclusion is a statement, which is claimed to follow from the given evidence (premise). In other words, the conclusion is the claim that an argument is trying to establish. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 43 Activity # 5: - Dear learners, can you now try to construct an argument based on the above definition of an argument? Let us now construct arguments together. Example-1: Example-2: 1) All Ethiopians are Africans. (Premise 1) 2) Some Africans are black. (Premise-1) Tsionawit is Ethiopian. (Premise2) Zelalem is an African. (Premise-2) Therefore, Tsionawit is African. (Conclusion) Therefore, Zelalem is black. (Conclusion) In both arguments, the first two statements are premises, because they are claimed to provide evidence for the third statement, whereas the third statement is a conclusion because it is claimed to follow from the given evidences. The claim that the premises support the conclusion, (and/or that the conclusion follow from the premises), is indicated by the word ‗‗therefore.‘‘ All arguments may be placed in one of two basic groups: those in which the premises really do support the conclusion and those in which they do not, even though they are claimed to. The former are said to be good (well-supported) arguments, the latter bad (poorly-supported) arguments. For example, compare the above two examples. In the first argument, the premises really do support the conclusion, they give good reason for believing that the conclusion is true, and therefore, the argument is a good one. But the premises of the second argument fail to support the conclusion adequately. Even if they may be true, they do not provide good reason to believe that the conclusion is true. Therefore, it is bad argument, but it is still an argument. But how can we distinguish premises from conclusion and vice versa? Despite the purpose of logic, as the science that evaluates and analyses arguments, is to develop methods and techniques that allow us to distinguish good arguments from bad, one of the most important tasks in the analysis of arguments is to distinguish premises from conclusion and vice versa. Sometimes identifying a conclusion from premises is very tough. Premises and conclusions are difficult to identify for a number of reasons. Even though all arguments are By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 44 ideally presumed to be composed of premises and a conclusion, in reality, sometimes arguments may contain other sentences as elements. Moreover, even though it is assumed, for the sake of argument, that all arguments are composed of premises and conclusion, identifying conclusion from argument is very difficult. Since it is impossible to analyze arguments without identifying a conclusion from premises, we need techniques that can help us to identify premises from a conclusion and vice versa. The first technique that can be used to identify premises from a conclusion and vice versa is looking at an indicator word. Frequently, arguments contain certain indicator words that provide clues in identifying premises and conclusion. Here below are some Conclusion Indicators: Therefore We may conclude Thus So Wherefore Entails that Consequently It follows that Accordingly Hence We may infer Provided that It shows that It implies that It must be that Whence As a result In argument that contains any of the conclusion indicator words, the statement that follows the indicator word can usually be identified as the conclusion. By the process of elimination, the other statements in the argument can be identified as premises, but only based on their logical importance to the identified conclusion. Example: Women are mammals. Zenebech is a woman. Therefore, Zenebech is a mammal. Based on the above rule, the conclusion of this argument is “Zenebech is a mammal‖ because it follows the conclusion indicator word ―therefore‖, and the other two statements are premises. If an argument does not contain a conclusion indicator, it may contain a premise indicator. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 45 Here below are some typical Premise Indicators: Since Seeing that In that As indicated by Given that May be inferred from Because As Inasmuch as Owing to For For the reason that In argument that contains any of the premise indicator words, a statement that follows the indicator word can usually be identified as a premise. By same the process of elimination, the other remaining single statement will be a conclusion. Example: You should avoid any form of cheating on exams because cheating on exams is punishable by the Senate Legislation of the University. Based on the above rule, the premise of this argument is “cheating on exams is punishable by the Senate Legislation of the University‖ because it follows the premise indicator word ―because‖, and the other statement is a premise. One premise indicator not included in the above list is ‗‗for this reason.‘‘ This indicator is special in that it comes immediately after the premise it indicates and before the conclusion. We can say that in the middle place between the premise and the conclusion, this indicator can be both premise and conclusion indicator. The statement that comes before ‗‗for this reason‘‘ is the premise of an argument and the statement that comes after ―for this reason‖ is the conclusion. One should be careful not to confuse ‗‗for this reason‘‘ with ‗‗for the reason that.‘‘ Sometimes a single indicator can be used to identify more than one premise. Consider the following argument: Tsionawit is a faithful wife, for Ethiopian women are faithful wives and Tsionawit an Ethiopian. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 46 The premise indicator ‗‗for‘‘ goes with both ‗‗Ethiopian women are faithful wives‘‘ and ‗‗Tsionawit is an Ethiopian”. These are the premises. By process of elimination, ‗‗Tsionawit is a faithful wife‖ is the conclusion. Sometimes you may an argument that contains no indicator all: neither a conclusion indicator word nor a premise indicator word. When this occurs, the reader/ listener must ask himself or herself such questions as:  What single statement is claimed (implicitly) to follow from the others?  What is the arguer trying to prove?  What is the main point in the passage? The answers to these questions should point to the conclusion. Example: Our country should increase the quality and quantity of its military. Ethnic conflicts are recently intensified; boarder conflicts are escalating; international terrorist activities are increasing. The main point of this argument is to show that the country should increase the size and quality of its military. All the rest are given in support of the conclusion. As you can see there are no indicator words. The following is the standard form of this argument: Ethnic conflicts are recently intensified. (P-1) Boarder conflicts are escalating. (P-2) International terrorist activities are increasing. (P-3) Thus, the country should increase the quality and quantity of its military. (C) Passages that contain arguments sometimes contain statements that are neither premises nor conclusion. Only statements that are actually intended to support the conclusion should be included in the list of premises. If a statement has nothing to do with the conclusion or, for example, simply makes a passing comment, it should not be included within the context of the argument. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 47 Example: Socialized medicine is not recommended because it would result in a reduction in the overall quality of medical care available to the average citizen. In addition, it might very well bankrupt the federal treasury. This is the whole case against socialized medicine in a nutshell. The conclusion of this argument is ‗‗Socialized medicine is not recommended,‘‘ and the two statements following the word ‗‗because‘‘ are the premises. The last statement makes only a passing comment about the argument itself and is therefore neither a premise nor a conclusion. Inference is another concept. In the narrower sense it means the reasoning process expressed by the argument. And broadly it refers the argument itself. For the purpose of this course, we use the narrower sense of the term inference or inferential link between the premises and the conclusion of arguments. Lesson 2: Techniques of Recognizing Arguments Lesson Overview An argument is a systematic combination of one or more than one statements, which are claimed to provide a logical support or evidence (i.e., premise(s) to another single statement which is claimed to follow logically from the alleged evidence (i.e., conclusion). However, not all passages that contain two or more statements are argumentative. There are various passages that contain two or more statements but are not argumentative. Argumentative arguments are distinguished from such kind of passages by their primary goal: proving something. In this lesson, we will see the techniques of distinguishing argumentative passages from non- argumentative passages. Lesson Objectives: After the accomplishment of this lesson, you will be able to:  Recognize argumentative passages.  Recognize non-argumentative passages.  Distinguish argumentative passages from non-argumentative passages.  Understand the concepts inferential claim and factual claim. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 48 2.1 Recognizing Argumentative Passages Activity # 1: - Dear learners, what do you think are argumentative passages? What qualifies a passage to be an argument? Evaluating arguments about different issues in human life like those that address, religion, politics, ethics, sport, science, love, culture, environment, society, culture etc. is the central concern of logic. Therefore, as logicians, in order to evaluate arguments easily, we need to understand the nature of arguments and further we need to understand what argument is not, because not all passages contain argument. Since logic deals with arguments, it is important for students to develop the ability to identify whether passages contain an argument. In a general way, a passage contains an argument if it purports to prove something; if it does not do so, it does not contain an argument. But what does it mean to purport to prove something? Two conditions must be fulfilled for a passage to purport to prove something: 1) At least one of the statements must claim to present evidence or reasons. 2) There must be a claim that the alleged evidence or reasons supports or implies something- that is, a claim that something follows from the alleged evidence. As we have seen earlier, the statements that claim to present the evidence or reasons are the premises and the statement that the evidence is claimed to support or imply is the conclusion. Hence, the first condition refers to premises as it tries to provide or claim to provide reasons or evidences for the conclusion; and the second condition refers to a conclusion. It is not necessary that the premises present actual evidence or true reasons nor that the premises actually do support the conclusion. But at least the premises must claim to present evidence or reasons, and there must be a claim that the evidence or reasons support or imply something. The first condition expresses a factual claim, and deciding whether it is fulﬁlled often falls outside the domain of logic. Thus, most of our attention will be concentrated on whether the second condition is fulfilled. The second condition expresses what is called an inferential claim. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 49 The inferential claim is simply the claim that the passage expresses a certain kind of reasoning process- that something supports or implies something or that something follows from something. Also, you should recognize that this claim is not equitable with the intentions of the arguer. Intentions are subjective and, as such, are usually not accessible to the evaluator. Rather, the inferential claim is an objective feature of an argument grounded in its language or structure. In evaluating arguments, therefore, most of our attention will be concentrated on whether the second condition is fulfilled because it is not necessary, at least at this level, that the premises present actual evidence or true reasons nor that do the premises actually support the conclusion. An inferential claim can be either explicit or implicit. An explicit inferential claim is usually asserted by premise or conclusion indicator words (‗‗thus,‘‘ ‗‗since,‘‘ ‗‗because,‘‘ ‗‗hence,‘‘ ‗‗therefore,‘‘ and so on). It exists if there is an indicator word that asserts an explicit relationship between the premises and the conclusions. Example: Gamachuu is my biological father, because my mother told so. In this example, the premise indicator word ―because‖ expresses the claim that evidence supports something, or that evidence is provided to prove something. Hence, the passage is an argument. An implicit inferential claim exists if there is an inferential relationship between the statements in a passage, but the passage contains no indicator words. Example: The genetic modification of food is risky business. Genetic engineering can introduce unintended changes into the DNA of the food-producing organism, and these changes can be toxic to the consumer. The inferential relationship between the ﬁrst statement and the other two constitutes an implicit claim that evidence supports something, so we are justiﬁed in calling the passage an argument though it does not contain indicator word. The ﬁrst statement is the conclusion, and the other two are the premises. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 50 Sometimes it is difficult to identify whether a passage contain an argument. In deciding whether there is a claim that evidence supports or implies something keep an eye out for (1) indicator words, and (2) the presence of an inferential claim between the statements. In connection with these points, however, a word of caution is in order. First, the mere occurrence of an indicator word by no means guarantees the presence of an argument. The presence of an indicator word does not mean that the existing indicator word actually and always indicate a premises or a conclusions. Thus, before deciding that an indicator word indicates a premises or a conclusion, make sure that the existing indicator word is used to indicate a premise or a conclusion. Example: Since Edison invented the phonograph, there have been many technological developments. Since Edison invented the phonograph, he deserves credit for a major technological development. In the first passage the word ‗‗since‘‘ is used in a temporal sense. It means ‗‗from the time that.‘‘ Thus, the first passage is not an argument. In the second passage ‗‗since‘‘ is used in a logical sense, and so the passage is an argument. Second, it is not always easy to detect the occurrences of an inferential relationship between statements in a passage, and the reader may have to review a passage several times before making a decision. Therefore, in deciding whether a passage contains an argument one should try to insert mentally some indicators words among the statements to see whether there is a flow of ideas among the statements. Even with this mental experiment, however, deciding whether a passage contains an argument is very difficult. As a result, not everyone will agree about every passage. Sometimes the only answer possible is a conditional one: ―If this passage contains an argument, then these are the premises and that is the conclusion.‖ To assists in distinguishing passages that contain arguments from those that do not, it is important to identify passages, which do not contain arguments: Non-argumentative passages. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 51 2.2 Recognizing Non-argumentative Passages Activity # 2: - Dear learners, what do you think are non-argumentative passages? What do they lack to be arguments? Having seen what arguments are and how we recognize them, we will now focus on what arguments are not and how we recognize them. Non-argumentative passages are passages, which lack an inferential claim. These include simple non-inferential passages, expository passages, illustrations, explanations, and conditional statements. Passages that lack an inferential claim may be statements, which could be premises, conclusion, or both. What is missed is a claim that a reasoning process is being made. As was discussed previously, for a passage to be an argument, it not only should contain premises and a conclusion but also an inferential claim or a reasoning process. In this portion of our lesson, we will discuss some of the most important forms of non-argumentative passages. Simple Non-inferential Passages Simple non-inferential passages are unproblematic passages that lack a claim that anything is being proved. Such passages contain statements that could be premises or conclusions (or both), but what is missing is a claim that any potential premise supports a conclusion or that any potential conclusion is supported by premises. Passages of this sort include warnings, pieces of advice, statements of belief or opinion, loosely associated statements, and reports. A warning is a form of expression that is intended to put someone on guard against a dangerous or detrimental situation. Example: Whatever you promise to tell, never confide political secrets to your wife. In this passage, no evidence is given to prove that the statement is true; and if no evidence is given to prove that the statement is true, then there is no argument. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 52 A piece of advice is a form of expression that makes a recommendation about some future decision or course of conduct. Example: After class hours, I would suggest that you give careful consideration to the subject matter you have discussed. As with warnings, there is no evidence that is intended to prove anything in piece of advices, and hence there is no argument in the above passage. A statement of belief or opinion is an expression about what someone happens to believe or think about something. Example: We believe that our university must develop and produce outstanding students who will perform with great skill and fulfill the demands of our nation. This passage does not make any claim that the belief or opinion is supported by evidence, or that it supports some conclusion, and hence does not contain an argument. Loosely associated statements may be about the same general subject, but they lack a claim that one of them is proved by the others. Example: Not to honor men of worth will keep the people from contention; not to value goods that are hard to come by will keep them from theft; not to display what is desirable will keep them from being unsettled of mind. (Lao-Tzu, Thoughts from the Tao Te Ching) Because there is no claim that any of these statements provides evidence or reasons for believing another, there is no argument. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 53 A report consists of a group of statements that convey information about some topic or event. Example: The great renaissance dam of Ethiopia has opened an employment opportunity for thousands of Ethiopians. In its completion, thirteen thousand Ethiopians are expected to be hired. These statements could serve as the premises of an argument, but because the author makes no claim that they support or imply anything, there is no argument. One must be careful, though, with reports about arguments. Example: “The Air Force faces a serious shortage of experienced pilots in the years ahead, because repeated overseas tours and the allure of high paying jobs with commercial airlines are winning out over lucrative bonuses to stay in the service,” says a prominent Air Force official. (Newspaper clipping) Properly speaking, this passage is not an argument, because the author of the passage does not claim that anything is supported by evidence. Rather, the author reports the claim by the Air Force oﬃcial that something is supported by evidence. If such passages are interpreted as ―containing‖ arguments, it must be made clear that the argument is not the author‘s but one made by someone about whom the author is reporting. Expository Passages An expository passage is a kind of discourse that begins with a topic sentence followed by one or more sentences that develop the topic sentence. If the objective is not to prove the topic sentence but only to expand it or elaborate it, then there is no argument. Example: There is a stylized relation of artist to mass audience in the sports, especially in baseball. Each player develops a style of his own-the swagger as he steps to the plate, the unique windup a By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 54 pitcher has, the clean-swinging and hard-driving hits, the precision quickness and grace of infield and outfield, the sense of surplus power behind whatever is done. (Max Lerner, America as a Civilization) In this passage the topic sentence is stated ﬁrst, and the remaining sentences merely develop and ﬂesh out this topic sentence. This passage is not argument, because it lacks an inferential claim. However, expository passages diﬀer from simple non-inferential passages (such as warnings and pieces of advice) in that many of them can also be taken as arguments. If the purpose of the subsequent sentences in the passage is not only to ﬂesh out the topic sentence but also to prove it, then the passage is an argument. Example: Skin and the mucous membrane lining the respiratory and digestive tracts serve as mechanical barriers to entry by microbes. Oil gland secretions contain chemicals that weaken or kill bacteria on skin. The respiratory tract is lined by cells that sweep mucus and trapped particles up into the throat, where they can be swallowed. The stomach has an acidic pH, which inhibits the growth of many types of bacteria. (Sylvia S. Mader, Human Biology, 4th ed.) In this passage, the topic sentence is stated ﬁrst, and the purpose of the remaining sentences is not only to show how the skin and mucous membranes serve as barriers to microbes but also to prove that they do this. Thus, the passage can be taken as both an expository passage and an argument. In deciding whether an expository passage should be interpreted as an argument, try to determine whether the purpose of the subsequent sentences in the passage is merely to develop the topic sentence or also to prove that it is true. In borderline cases, ask yourself whether the topic sentence makes a claim that everyone accepts or agrees with. If it does, the passage is probably not an argument. In real-life situations, authors rarely try to prove something is true when everyone already accepts it. However, if the topic sentence makes a claim that many people do not accept or have never thought about, then the purpose of the remaining sentences may be both By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 55 to prove the topic sentence is true as well as to develop it. If this be so, the passage is an argument. Finally, if even this procedure yields no deﬁnite answer, the only alternative is may be to say that if the passage is taken as an argument, then the ﬁ rst statement is the conclusion and the others are the premises. Illustrations An illustration is an expression involving one or more examples that is intended to show what something means or how it is done. Illustrations are often confused with arguments because many illustrations contain indicator words such as ―thus.‖ Example: Chemical elements, as well as compounds, can be represented by molecular formulas. Thus, oxygen is represented by “O2”, water by “H2O”, and sodium chloride by “NaCl”. This passage is not an argument, because it makes no claim that anything is being proved. The word ―thus‖ indicates how something is done - namely, how chemical elements and compounds can be represented by formulas. However, as with expository passages, many illustrations can be taken as arguments. Such arguments are often called arguments from example. Here is an instance of one: Although most forms of cancer, if untreated, can cause death, not all cancers are life- threatening. For example, basal cell carcinoma, the most common of all skin cancers, can produce disfigurement, but it almost never results in death. In this passage, the example given is intended to prove the truth of ―Not all cancers are life- threatening.‖ Thus, the passage is best interpreted as an argument. In deciding whether an illustration should be interpreted as an argument, determine whether the passage merely shows how something is done or what something means, or whether it also purports to prove something. In borderline cases, it helps to note whether the claim being illustrated is one that practically everyone accepts or agrees with. If it is, the passage is probably By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 56 not an argument. As already noted, in real-life situations, authors rarely attempt to prove what everyone already accepts. But if the claim being illustrated is one that many people do not accept or have never thought about, then the passage may be interpreted as an argument. Thus, in reference to the ﬁrst example we considered, most people are aware that elements and compounds can be expressed by formulas. For example, practically everyone knows that water is H2O. But they may not have ever considered whether some forms of cancer are not life- threatening. This is one of the reasons for evaluating the ﬁrst example as mere illustration and the last one as an argument. Explanations One of the most important kinds of non-argument is the explanation. An explanation is an expression that purports to shed light on some event or phenomenon, which is usually accepted as a matter of fact. It attempts to clarify, or describe such alike why something is happen that way or why something is what it is. Example: Cows digest grass while humans cannot, because their digestive systems contain enzyme not found in humans. Every explanation is composed of two distinct components: the explanandum and explanans. The explanandum is the statement that describes the event or phenomenon to be explained, and the explanans is the statement or group of statements that purports to do the explaining. In the ﬁrst example, the explanandum is the statement ―Cows digest grass while humans cannot‖ and the explanans is ―their [cows‟] digestive systems contain enzyme not found in humans.‖ Argument Explanation Premise Accepted fact Explanans Claimed to prove Claimed to shed light on Conclusion Explanations By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 57 Accepted fact Explanations are sometimes mistaken for arguments because they often contain the indicator word ―because.‖ Yet explanations are not arguments, because in an explanation the purpose of the explanans is to shed light on, or to make sense of, the explanandum event, not to prove that it occurred. In other words, the purpose of the explanans is to show why something is the case, whereas in an argument, the purpose of the premises is to prove that something is the case. That is, the premise refer to an accepted fact, and intended to prove that something is the case, while the conclusion is a new assertion followed from the already known fact. Moreover, in explanation, we precede backward from fact to the cause whereas in argument we move from premise to the conclusion. In the above example given, the fact that cows digest grass but humans cannot is readily apparent to everyone. The statement that cows‘ digestive systems contain enzyme not found in humans is not intended to prove that cows digest grass but humans cannot, but rather to show why it is so. Explanations bear a certain similarities to an argument. The rational link between the explanandum and explanans may at times resemble the inferential link between the premise and the conclusion of an argument. Thus, to distinguish explanations from arguments, first identify the statement that is either the explanandum or the conclusion (usually this is the statement that precedes the word ―because‖). If this statement describes an accepted matter of fact, and if the remaining statements purport to shed light on this statement, then the passage is an explanation. This method usually works to distinguish arguments from explanations. However, some passages can be interpreted as both explanations and arguments. Example: Women become intoxicated by drinking a smaller amount of alcohol than men because men metabolize part of the alcohol before it reaches the bloodstream, whereas women do not. The purpose of this passage could be to prove the ﬁrst statement to those who do not accept it as fact, and to shed light on that fact to those who do accept it. Alternately, the passage could be By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 58 intended to prove the ﬁrst statement to a person who accepts its truth on blind faith or incomplete experience, and simultaneously to shed light on this truth. Thus, this passage can be correctly interpreted as both an explanation and an argument. Perhaps the greatest problem confronting the eﬀort to distinguish explanations from arguments lies in determining whether something is an accepted matter of fact. Obviously, what is accepted by one person may not be accepted by another. Thus, the eﬀort often involves determining which person or group of people the passage is directed to- the intended audience. Sometimes the source of the passage (textbook, newspaper, technical journal, etc.) will decide the issue. But when the passage is taken totally out of context, ascertaining the source may prove impossible. In those circumstances the only possible answer may be to say that if the passage is an argument, then such-and-such is the conclusion and such-and-such are the premises. Conditional Statements A conditional statement is an ―if... then...‖ statement. Example: If you study hard, then you will score „A‟ grade. Every conditional statement is made up of two component statements. The component statement immediately following the ―if‖ is called the antecedent (if-clause), and the one following the ―then‖ is called the consequent (then-clause). However, there is an occasion that the order of antecedent and consequent is reversed. That is, when occasionally the word ‗‗then‘‘ is left out, the order of antecedent and consequent is reversed. For example if we left out ―then‖ from the above example the antecedent and consequent is reversed: You will score „A‟ grade if you study hard. In the above example, the antecedent is ―You study hard,‖ and the consequent is ―You will score „A‟ grade.‖ In this example, there is a meaningful relationship between antecedent and consequent. However, such a relationship need not exist for a statement to count as conditional. The statement ―If Getaneh Kebede is a singer, then Hawassa is in Mekelle‖ is just as much a conditional statement as that in the above example. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 59 Conditional Statements: Antecedent Consequent If ---------------------------- then ---------------------------------. Consequent Antecedent ---------------------------- if ---------------------------------. Conditional statements are not arguments, because they fail to meet the criteria given earlier. In an argument, at least one statement must claim to present evidence, and there must be a claim that this evidence implies something. In a conditional statement, there is no claim that either the antecedent or the consequent presents evidence. In other words, there is no assertion that either the antecedent or the consequent is true. Rather, there is only the assertion that if the antecedent is true, then so is the consequent. For example, the above example merely asserts that if you study hard, then you will score ‗A‘. It does not assert that you study hard. Nor does it assert you scored ‗A‘. Of course, a conditional statement as a whole may present evidence because it asserts a relationship between statements. Yet when conditional statements are taken in this sense, there is still no argument, because there is then no separate claim that this evidence implies anything. Therefore, a single conditional statement is not an argument. The fact that a statement begin with ―if‖ makes it the idea conditional and not a final reasonable assertion. That is why also conditional statements are not evaluated as true or false without separately evaluating the antecedent and the consequent. They only claim that if the antecedent is true then so is the consequent. However, some conditional statements are similar to arguments in that they express the outcome of a reasoning process. As such, they may be said to have a certain inferential content. Consider the following example: If destroying a political competitor gives you joy, then you have a low sense of morality. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 60 The link between the antecedent and consequent resembles the inferential link between the premises and conclusion of an argument. Yet there is a diﬀerence because the premises of an argument are claimed to be true, whereas no such claim is made for the antecedent of a conditional statement. Accordingly, conditional statements are not arguments. Yet, although taken by themselves are not arguments, their inferential content, (the inferential content between the antecedent and the consequent), may be re-expressed to form arguments. For example, the conditional statement can be re-expressed to form an argument as follows: Destroying a political competitor gives you joy. Therefore, you have a low sense of morality. Here, we clearly have a premise and conclusion structure, and the conclusion is asserted on the basis of the premise. Therefore, it is argument. Finally, while no single conditional statement is an argument, a conditional statement may serve as either the premise or the conclusion (or both) of an argument. Observe the following examples: If he is selling our national secretes to enemies, then he is a traitor. He is selling our national secretes to enemies. Therefore, he is a traitor. If he is selling our national secretes to enemies, then he is a traitor. If he is a traitor, then he must be punished by death. Therefore, If he is selling our national secretes to enemies, then he must be punished by death. The relation between conditional statements and arguments may now be summarized as follows: 1) A single conditional statement is not an argument. 2) A conditional statement may serve as either the premise or the conclusion (or both) of an argument. 3) The inferential content of a conditional statement may be re-expressed to form an argument. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 61 The first two rules are especially pertinent to the recognition of arguments. According to the ﬁrst rule, if a passage consists of a single conditional statement, it is not an argument. But if it consists of a conditional statement together with some other statement, then, by the second rule, it may be an argument, depending on such factors as the presence of indicator words and an inferential relationship between the statements. Conditional statements are especially important in logic (and many other ﬁelds) because they express the relationship between necessary and sufficient conditions. A is said to be a sufficient condition for B whenever the occurrence of A is all that is needed for the occurrence of B. For example, being a dog is a sufficient condition for being an animal. On the other hand, B is said to be a necessary condition for A whenever A cannot occur without the occurrence of B. Thus, being an animal is a necessary condition for being a dog. The difference between sufficient and necessary conditions is a bit tricky. So, to clarify the idea further, suppose you are given a large, closed cardboard box. Also, suppose you are told that there is a dog in the box. Then you know for sure, there is an animal in the box. No additional information is needed to draw this conclusion. This means that being a dog is sufficient for being an animal. However, being a dog is not necessary for being an animal, because if you are told that the box contains a cat, you can conclude with equal certainty that it contains an animal. In other words, it is not necessary for the box to contain a dog for it to contain an animal. It might equally well contain a cat, a mouse, a squirrel, or any other animal. On the other hand, suppose you are told that whatever might be in the box, it is not an animal. Then you know for certain there is no dog in the box. The reason you can draw this conclusion is that being an animal is necessary for being a dog. If there is no animal, there is no dog. However, being an animal is not sufficient for being a dog, because if you are told that the box contains an animal, you cannot, from this information alone, conclude that it contains a dog. It might contain a cat, a mouse, a squirrel, and so on. These ideas are expressed in the following conditional statements: If X is a dog, then X is an animal. If X is not an animal, then X is not a dog. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 62 The ﬁrst statement says that being a dog is a sufficient condition for being an animal, and the second that being an animal is a necessary condition for being a dog. However, a little reﬂection reveals that these two statements say exactly the same thing. Thus, each expresses in one way a necessary condition and in another way a sufficient condition. A is a sufficient condition for B; if A occurs, then B must occur. Note: A is a necessary condition for B; if B occur, then A must occur. In general, non-argumentative passages may contain components that resemble the premises and conclusions of arguments, but they do not have an inferential claim. However, some passages like expository passages, illustrations, and explanations can be interpreted as arguments; and the inferential contents of conditional statements may be re-expressed to form arguments. Therefore, in deciding whether a passage contains an argument, you should look for three things: 1) indicator words such as “therefore,” “since,” “because,” and so on; 2) an inferential relationship between the statements; and 3) typical kinds of non-arguments. But remember that the mere occurrence of an indicator word does not guarantee the presence of an argument. You must check to see that the statement identiﬁed as the conclusion is claimed to be supported by one or more of the other statements. Also keep in mind that in many arguments that lack indicator words, the conclusion is the ﬁrst statement. Furthermore, it helps to mentally insert the word ―therefore‖ before the various statements before deciding that a statement should be interpreted as a conclusion. Lesson 3: Types of Arguments: Deduction and Induction Lesson Overview In our previous lesson, we saw that every argument involves an inferential claim- the claim that the conclusion is supposed to follow from the premises. Every argument makes a claim that its premises provide grounds for the truth of its conclusion. The question we now address has to do By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 63 with the strength of this claim. Just how strongly is the conclusion claimed to follow from the premises. The reasoning process (inference) that an argument involves is expressed either with certainty or with probability. That is what the logician introduced the name deduction and induction for, respectively. If the conclusion is claimed to follow with strict certainty or necessity, the argument is said to be deductive; but if it is claimed to follow only probably, the argument is said to be inductive. Therefore, a conclusion may be supported by its premise in two very different ways. These two different ways are the two great classes of arguments: Deductive arguments and Inductive arguments. And the distinction between these two classes of arguments, because every argument involves an inferential claim, lies in the strength of their inferential claim. Understanding the distinction of these classes is essential in the study of logic. In this lesson, we will learn the broad groups of arguments, Deductive arguments and Inductive arguments, and the techniques of distinguishing one from the other. Lesson Objectives: After the successful accomplishment of this lesson, you will be able to:  Understand the meaning, nature, and forms of a deductive argument.  Understand the meaning, nature, and forms of an inductive argument.  Distinguish deductive arguments from inductive arguments, and vice versa. 3.1 Deductive Arguments Activity # 1: - Dear learners, how do you define a deductive argument? A deductive argument is an argument incorporating the claim that it is impossible for the conclusion to be false given that the premises are true. It is an argument in which the premises are claimed to support the conclusion in such a way that it is impossible for the premises to be true and the conclusion false. In such arguments, the conclusion is claimed to follow necessarily (conclusively) from the premises. Thus, deductive arguments are those that involve necessary reasoning. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 64 Example-1: Example-2: All philosophers are critical thinkers. All African footballers are blacks. Socrates is a philosopher. Messi is an African footballer. Therefore, Socrates is a critical thinker. It follows that, Messi is black. The above two examples are examples of a deductive argument. In both of them, the conclusion is claimed to follow from the premises with certainty; or the premises are claimed to support their corresponding conclusion with a strict necessity. If we, for example, assume that all philosophers are critical thinkers and that Socrates is a philosopher, then it is impossible that Socrates not be a critical thinker. Similarly, if we assume that all African footballers are blacks and that Messi is an African footballer, then it is impossible that Messi not be a black. Thus, we should interpret these arguments as deductive. 3.2 Inductive Arguments Activity # 2: - Dear learners, how do you define an inductive argument? An inductive argument is an argument incorporating the claim that it is improbable for the conclusion to be false given that the premises are true.. It is an argument in which the premises are claimed to support the conclusion in such a way that it is improbable for the premises to be true and the conclusion false. In such arguments, the conclusion is claimed to follow only probably from the premises. The premises may provide some considerable evidence for the conclusion but they do not imply (necessarily support) the conclusion. In this case, we might have sufficient condition (evidence) but we cannot be certain about the truth of the conclusion. However, this does not mean that the conclusion is wrong or unacceptable, where as it could be correct or acceptable but only based on probability. Thus, inductive arguments are those that involve probabilistic reasoning. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) Page 65 Example-1: Example-2: Most African leaders are blacks. Almost all women are mammals. Mandela was an African leader. Hanan is a woman. Therefore, probably Mandela was black. Hence, Hanan is a mammal. Both of the above arguments are inductive. In both of them, the conclusion does not follow from the premises with strict necessity, but it does follow with some degree of probability. That is, the conclusion is claimed to follow from the premises only probably; or the premises are claimed to support their corresponding conclusion with a probability. In other words, if we assume that the premises are true, then based on that assumption it is probable that the conclusion is true. If we, for example, assume that most African leaders were blacks and that Mandela was an African leader, then it is improbable that Mandela not been a black, or it is probable that Mandela was black. But it is not impossible that Mandela not been a black. Similarly, if we assume that almost all women are mammals and that Hanan is a woman, then it is improbable that Hanan not be a mammal, or it is probable that Hanan is a mammal. But it is not impossible that Hanan not be a mammal. Thus, the above arguments are best interpreted as inductive. 3.3 Differentiating Deductive and Inductive Arguments Activity # 3: - Dear learners, how do you distinguish a deductive argument from an inductive argument, and vice versa? Dear learners, we have said earlier that the distinction between inductive and deductive arguments lies in the strength of an argument‘s inferential claim. In other words, the distinction lies on how strongly the conclusion is claimed to follow from the premises, or how strongly the premises are claimed to support the conclusion. However, in most arguments, the strength of this claim is not explicitly stated, so we must use our interpretative abilities to evaluate it. In the deciding whether an argument is deductive or inductive, we must look at certain objective features of the argument. There are three factors that influence the decision about the deductiveness or inductiveness of an argument‘s inferential claim. These are: By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 66 1) The occurrence of special indicator words, 2) The actual strength of the inferential link between premises and conclusion, and 3) The character or form of argumentation the arguers use. However, we must acknowledge at the outset that many arguments in ordinary language are incomplete, and because of this, deciding whether the argument should best be interpreted as deductive or inductive may be impossible. Let us see the above factors in detail in order to understand and identify the different styles of argumentation. The first factor that influences our decision about a certain inferential claim is the occurrence of special indicator words. There are different sort of indicator words that indicate or mark the type of a certain argument. Arguments may contain some words that indicate the arguer‘s certainty and confidence, or the arguer‘s uncertainty or doubt, about the truth of his/her conclusion. Words like ―certainly,‘‘ ―necessarily,‖ ‗‗absolutely,‘‘ and ‗‗definitely‘‘ indicate that the argument should be taken as deductive, whereas words like, ―probable‖ ‗‗improbable,‘‘ ‗‗plausible,‘‘ ‗‗implausible,‘‘ ‗‗likely,‘‘ ‗‗unlikely,‘‘ and ‗‗reasonable to conclude‖ suggest that an argument is inductive. The point is that if an argument draws its conclusion, using either of the deductive indicator words, it is usually best to interpret it as deductive, but if it draws its conclusion, using either of the inductive indicator words, it is usually best to interpret it as inductive. (Note that the phrase ‗‗it must be the case that‘‘ is ambiguous; ‗‗must‘‘ can indicate either probability or necessity). Deductive and Inductive indicator words often suggest the correct interpretation. However, one should be cautious about these special indicator words, because if they conflict with one of the other criteria, we should probably ignore them. For arguers often use phrases such as ‗‗it certainly follows that‘‘ for rhetorical purposes to add impact to their conclusion and not to suggest that the argument be taken as deductive. Similarly, some arguers, not knowing the distinction between inductive and deductive, will claim to ‗‗deduce‘‘ a conclusion when their argument is more correctly interpreted as inductive. If one takes these words at face value, then one might wrongly leads into wrong conclusions. Therefore, the occurrence of an indicator word By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 67 is not a certain guarantee for the deductiveness or inductiveness of an argument unless it is supported by the other features. This leads us to consider the second factor. The second factor that bears upon our interpretation of an argument as inductive or deductive is the actual strength of the inferential link between premises and conclusion. If the conclusion actually does follow with strict necessity from the premises, the argument is clearly deductive. In such an argument, it is impossible for the premises to be true and the conclusion false. If, on the other hand, the conclusion of an argument does not follow with strict necessity but does follow probably, it is usually best to interpret it as inductive argument. Consider the following examples. Example-1: Example-2: All Ethiopian people love their country. The majority of Ethiopian people are poor. Debebe is an Ethiopian. Alamudin is an Ethiopian. Therefore, Debebe loves his country. Therefore, Alamudin is poor. In the ﬁrst example, the conclusion follows with strict necessity from the premises. If we assume that all Ethiopian people love their country and that Debebe is an Ethiopian, then it is impossible that Debebe not love his country. Thus, we should interpret this argument as deductive. In the second example, the conclusion does not follow from the premises with strict necessity, but it does follow with some degree of probability. If we assume that the premises are true, then based on that assumption it is probable that the conclusion is true. Thus, it is best to interpret the second argument as inductive. Occasionally, an argument contains no special indicator words, and the conclusion does not follow either necessarily or probably from the premises; in other words, it does not follow at all. This situation points up the need for the third factor to be taken into account, which is the character or form of argumentation the arguer uses. Let us see some examples of deductive argumentative forms and inductive argumentative forms. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 68 Instances of Deductive Argumentative Forms Many arguments have a distinctive character or form that indicates that the premises are supposed to provide absolute support for the conclusion. Five examples of such forms or kinds of argumentation are arguments based on mathematics, arguments from deﬁnition, and syllogisms: categorical, hypothetical, and disjunctive syllogisms. Argument based on mathematics: it is an argument in which the conclusions depend on some purely arithmetic or geometric computation or measurement. For example, you can put two orange and three bananas in a bag and conclude that the bag contains five fruits. Or again you can measure a square pieces of land and after determining it is ten meter on each side conclude that its area is a hundred square meter. Since all arguments in pure mathematics are deductive, we can usually consider arguments that depend on mathematics to be deductive as well. A noteworthy exception, however, is arguments that depend on statistics are usually best interpreted as inductive. Arguments based on definition: it is an argument in which the conclusion is claimed to depend merely up on the definition of some words or phrase used in the premise or conclusion. For example, one may argue that Angel is honest; it is follows that Angel tells the truth. Or again, Kebede is a physician; therefore, he is a doctor. These arguments are deductive because their conclusions follow with necessity from the definitions ―honest‖ and ―physician‖. Syllogisms are arguments consisting of exactly two premises and one conclusion. Syllogisms can be categorized into three groups; categorical, hypothetical, and disjunctive syllogism. Categorical syllogism: a syllogism is an argument consisting of exactly two premises and one conclusion. Categorical syllogism is a syllogism in which the statement begins with one of the words ―all‖, ―no‖ and ―some‖. Example: All Egyptians are Muslims. No Muslim is a Christian. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 69 Hence, no Egyptian is a Christian. Arguments such as these are nearly interpreted as deductive. Hypothetical syllogism: It is a syllogism having a conditional statement for one or both of its premises. Example: If you study hard, then you will graduate with Distinction. If you graduate with Distinction, then you will get a rewarding job. Therefore, if you study hard, then you will get a rewarding job. Such arguments are best interpreted as deductive. Disjunctive syllogism: it is a syllogism having a disjunctive statement. (I.e. an ―either … or‖ statement.) Example: Rewina is either Ethiopian or Eritrean. Rewina is not Eritrean. Therefore, Rewina is Ethiopian. As with hypothetical syllogism, such arguments are usually best taken as deductive. Instances of Inductive Argumentative Forms In general, inductive arguments are such that the content of the conclusion is in some way intended to ―go beyond‖ the content of the premises. The premises of such an argument typically deal with some subject that is relatively familiar, and the conclusion then moves beyond this to a subject that is less familiar or that little is known about. Such an argument may take any of several forms: predictions about the future, arguments from analogy, inductive generalizations, arguments from authority, arguments based on signs, and causal inferences, to name just a few. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 70 Prediction: in a prediction the premises deals with some known event in the present or the past and the conclusions moves beyond this event to some event to relative future. For example, one may argue that because certain clouds develop in the center of the highland, a rain will fall within twenty-four hours. Nearly everyone realizes that the future cannot be known with certainty. Thus, whenever an argument makes a prediction about the future one is usually justified considering the argument inductive. An argument from analogy: It is an argument that depends on the existence of an analogy or similarity between two things or state of affairs. Because of the existence of this analogy a certain conditions that affects the better- known thing or situations is concluded to affect the less familiar , lesser known-thing or situation. For instance, one may conclude, after observing the similarity of some features of Computer A and car B: that both are manufactured in 2012; that both are easy to access; that Computer A is fast in processing; it follows that Computer B is also fast in processing. This argument depends on the existence of a similarity or analogy between the two cars. The certitude attending such an inference is obviously probabilistic at best. An inductive generalization: it is an argument that proceeds from the knowledge of a selected sample to some claim about the whole group. Because the members of the sample have a certain characteristics, it is argued that all members of the group have the same characteristics. For example, one may argue that because three out of four people in a single prison are black, one may conclude that three-fourth of prison populations are blacks. This example illustrate the use of statistics in inductive argumentation. An argument from authority: it is an argument in which the conclusions rest upon a statement made by some presumed authority or witness. A lawyer, for instance, may argue that the person is guilty because an eyewitness testifies to that effect under oath. Or again one may argue that all matters are made up of a small particles called ―quarks‖ because the University Professor said so. Because the professor and the eyewitness could be either mistaken or lying, such arguments are essentially probabilistic. Arguments based on sign: it is an argument that proceeds from the knowledge of a certain sign to the knowledge of a thing or situation that the sign symbolizes. For instance, one may infer that By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 71 after observing ‗No Parking‘ sign posted on the side of a road, the area is not allowed for parking. But because the sign might be displaced or in error about the area or forgotten, conclusion follows only probably. A causal inference: it is an argument which proceed from the knowledge of a cause to the knowledge of an effect, or conversely, from the knowledge of an effect to knowledge of a cause. For example, from the knowledge that a bottle of water had been accidentally left in the freezer overnight, someone might conclude that it had frozen (cause to eﬀect). Conversely, after tasting a piece of chicken and ﬁnding it dry and tough, one might conclude that it had been overcooked (eﬀect to cause). Because specific instances of cause and effect can never be known with absolute certainty, one may usually interpret such an argument as inductive. Furthermore Considerations It should be noted that the various subspecies of inductive arguments listed here are not intended to be mutually exclusive. Overlaps can and do occur. For example, many causal inferences that proceed from cause to effect also qualify as predictions. We should take care not to confuse arguments in geometry, which are always deductive, with arguments from analogy or inductive generalizations. For example, an argument concluding that a triangle has a certain attribute (such as a right angle) because another triangle, with which it is congruent, also has that attribute might be mistaken for an argument from analogy. One broad classification of arguments not listed in this survey is scientific arguments. Arguments that occur in science can be either inductive or deductive, depending on the circumstances. In general, arguments aimed at the discovery of a law of nature are usually considered inductive. Another type of argument that occurs in science has to do with the application of known laws to specific circumstances. Arguments of this sort are often considered to be deductive, but only with certain reservations. A final point needs to be made about the distinction between inductive and deductive arguments. There is a tradition extending back to the time of Aristotle that holds that inductive arguments are those that proceed from the particular to the general, while deductive arguments are those By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 72 that proceed from the general to the particular. (A particular statement is one that makes a claim about one or more particular members of a class, while a general statement makes a claim about all the members of a class.) In fact, there are deductive arguments that proceed from the general to the general, from the particular to the particular, and from the particular to the general, as well as from the general to the particular; and there are inductive arguments that do the same. For example, here is a deductive argument that proceeds from the particular to the general: Three is a prime number. Five is a prime number. Seven is a prime number. Therefore, all odd numbers between two and eight are prime numbers. Here is an inductive argument that proceeds from the general to the particular: All emeralds previously found have been green. Therefore, the next emerald to be found will be green. In sum up, to distinguish deductive arguments from inductive, we look for special indicator words, the actual strength of the inferential link between premises and conclusion, and the character or form of argumentation. Lesson 4: Evaluating Arguments Lesson Overview In our previous lesson, we have seen that every argument makes two basic claims: a claim that evidence or reasons exist and a claim that the alleged evidence or reasons support something (or that something follows from the alleged evidence or reasons). The first is a factual claim, and the second is an inferential claim. The evaluation of every argument centers on the evaluation of these two claims. The most important of the two is the inferential claim, because if the premises fail to support the conclusion (that is, if the reasoning is bad), an argument is worthless. Thus, we will always test the inferential claim first, and only if the premises do support the conclusion will we test the factual claim (that is, the claim that the premises present genuine evidence, or are true). In this By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 73 lesson, we will be introduced with the central ideas and terminologies required to evaluate arguments. And the primary purpose of this lesson is to introduce you with the natures of good arguments both in deductive and inductive arguments. Hence, you will learn effective techniques and strategies for evaluating arguments. Lesson Objectives: After the successful accomplishment of this lesson, you will be able to:  Understand how to evaluate deductive arguments in terms of validity and soundness.  Recognize the relationship between truth value and validity.  Understand how to evaluate inductive arguments in terms of strength and cogency.  Recognize the relationship between truth value and strength. 4.1 Evaluating Deductive Arguments: Validity, Truth, and Soundness Activity # 1: - Dear learners, how do you think are validity and soundness? How do you think are the validity and soundness of a deductive argument evaluated? Deduction and Validity The previous section defined a deductive argument as one in which the premises are claimed to support the conclusion in such a way that if they are assumed true, it is impossible for the conclusions to be false. If the premises do in fact support the conclusions in this way the arguments is said to be valid; if not, it is invalid. Thus, a valid deductive argument is an argument such that if the premises are assumed true, it is impossible for the conclusion to be false. In such arguments, the conclusion follows with strict necessity from the premises. Conversely, an invalid deductive argument is an argument such that if the premises are assumed true, it is possible for the conclusion to be false. In these arguments, the conclusion does not follow with strict necessity from the premises, even though it is claimed to. Consider the following examples: Example-1: All men are mammals. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 74 All bulls are men. All philosophers are rational. Therefore, all bulls are mammals. Socrates was rational. Therefore, Socrates was a philosopher. Example-2: The first example is valid argument, because the conclusion actually followed from the premises with a strict necessity. If all men are assumed as mammals and bulls as men, then it is impossible for bulls not be mammals. Hence, the argument is valid. The second example is invalid argument, because the conclusion did not actually follow from the premises with a strict necessity, even though it is claimed to. That is, even if we assume that all philosophers rational and Socrates is rational, it is not actually impossible for Socrates not be a philosopher. The above definitions of valid and invalid arguments, along with their corresponding examples, lead us into two immediate conclusions. The first is that there is no middle ground between valid and invalid. An argument is either valid or invalid. The second consequence is that there is only an indirect relation between validity and truth. For an argument to be valid it is not necessary that either the premises or the conclusions be true, but merely that if the premises assumed true, it is impossible for the conclusion be false. That is, we do not have to know whether the premise of an argument is actually true in order to determine its validity (valid or invalid). To test an argument for validity, we begin by assuming that all premises are true, and then we determine if it is possible, in light of that assumption, for the conclusion to be false. Thus, the validity of argument is the connection between premise and conclusion rather than on the actual truth or falsity of the statement formed the argument. There are four possibilities with respect to the truth or falsity of the premises and conclusion of a given argument: 1) True premises and True conclusion, 2) True premises and False conclusion, 3) False premises and True conclusion, and 4) False premises and False conclusion. Note that all of the above possibilities, except the second case (true premises and false conclusion), allow for both valid and invalid arguments. That is, the second case does not allow By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 75 for valid arguments. As we have just seen, any argument having this combination is necessarily invalid. Let us discuss these possibilities in detail with examples. Validity and Truth Value Possibility # 1: A combination of True premises and True conclusion (the first case) allows for both valid and invalid arguments. Consider the following examples: Example-1 (Valid): Example-2 (Invalid): All women are mammals. (Tp) All philosophers are critical thinkers. (Tp) My mother is a mammal. (Tp) Plato was a critical thinker. (Tp) Therefore, my mother is a woman. (Tc) Therefore, Plato was a philosopher. (Tc) Based on the features of valid and invalid arguments, the above two examples, each of which combine True premises and True conclusion, are valid argument and invalid argument, respectively. Therefore, the first combination allows for both valid and invalid arguments. Possibility # 2: A combination of True premises and false conclusion (the second case) allows only for invalid arguments. Consider the following example: Example-1 (Invalid): All biologists are scientists. (Tp) John Nash was a scientist. (Tp) Therefore, John Nash was a biologist. (Fc) Based on the features of validity, the above example, which combines True premises and False conclusion, is an invalid argument. A valid argument with such combination does not exist. Any deductive argument having actually true premises and an actually false conclusion is invalid, because if the premises are actually true and the conclusion is actually false, then it certainly is possible for the premises to be true and the conclusion false. Thus, by definition, the argument is invalid. After all such combinations are contrary to the inferential claim of a deductive argument: By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 76 if the premises are assumed to be true, then it is impossible for the conclusion to be false. Therefore, the second combination allows only for invalid arguments. Possibility # 3: A combination of False premises and True conclusion (the third case) allows for both valid and invalid arguments. Consider the following examples: Example-1 (Valid): Example-2 (Invalid): All birds are mammals. (Fp) All birds are mammals. (Fp) All women are birds. (Fp) All ostriches are mammals. (Fp) Therefore, all women are mammals. (Tc) Therefore, all ostriches are birds. (Tc) Based on the features of valid and invalid arguments, the above two examples, each of which combine False premises and True conclusion, are valid argument and invalid argument, respectively. Therefore, the third combination, as the first one, allows for both valid and invalid arguments. Possibility # 4: A combination of False premises and False conclusion (the fourth case) allows for both valid and invalid arguments. Consider the following examples: Example-1 (Valid): Example-2 (Invalid): All Americans are Ethiopians. (Fp) All birds are mammals. (Fp) All Egyptians are Americans. (Fp) All ants are mammals. (Fp) Thus, all Egyptians are Ethiopians. (Fc) Therefore, all ants are birds. (Fc) Based on the features of valid and invalid arguments, the above two examples, each of which combine False premises and False conclusion, are valid argument and invalid argument, respectively. Therefore, the fourth combination also allows for both valid and invalid arguments. In general, the basic idea of evaluating deductive argument, validity (valid and invalid) is not something that is determined by the actual truth or falsity of the premises and conclusion. Rather, validity is something that is determined by the relationship between premises and conclusion. The question is not whether premises and conclusion are true or false, but whether the premises By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 77 support the conclusion. Nevertheless, there is one arrangement of truth and falsity in the premises and conclusion that does determine the issue of validity. Any deductive argument having actually true premises and an actually false conclusion is invalid for the reason given above. The idea that any deductive argument having actually true premises and a false conclusion is invalid may be the most important point in the entire system of deductive logic. The entire system of deductive logic would be quite useless if it accepted as valid any inferential process by which a person could start with truth in the premises and arrive at falsity in the conclusion. The relationship between the validity of a deductive argument and the truth and falsity of its premises and conclusions summarized as follows. Table 1.1 Premises Conclusion Validity True True Valid/invalid True False Invalid False True Valid/invalid False False Valid/invalid Deduction and Soundness We said earlier that the evaluation of every argument centers on the evaluation of two claims: the inferential claim and factual claim of the argument. We have also said that we will always test the inferential claim first, and only if the premises do support the conclusion will we test the factual claim (that is, the claim that the premises present genuine evidence, or are true). Now that we have tested the inferential claims of deductive arguments, it is time to proceed to the next step: evaluating the factual claims of deductive arguments. Depending on their actual ability, (assuming that they already have actually accomplished their inferential claims by being valid), to accomplish their factual claims, deductive arguments can be either sound or unsound. A sound argument is a deductive argument that is valid and has all true premises. Both conditions must be met for an argument to be sound, and if either is missing the By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 78 argument is unsound. A deductive argument that does not actually accomplish its inferential claim, (that is not valid), cannot be sound, regardless of the truth values of its premises. Such a deductive argument is unsound, by definition. Thus, an unsound argument is a deductive argument that is either valid with one or more false premises, or invalid, or both. Because a valid argument is one such that it is impossible for the premises to be true and the conclusion false, and because a sound argument does in fact have true premises, it follows that every sound argument, by definition, will have a true conclusion as well. A sound argument, therefore, is what is meant by a ‗‗good‘‘ deductive argument in the fullest sense of the term. Sound Argument = A valid argument + All true premises 4.2 Evaluating Inductive Arguments: Strength, Truth, and Cogency Activity # 2: - Dear learners, how do you think are strength and cogency? How do you think are the strength and cogency of an inductive argument evaluated? Induction and Strength The previous section defined an inductive argument as one in which the premises are claimed to support the conclusions in such a way that if they are assumed true, it is improbable for the conclusions to be false. If the premises do in fact support the conclusions in this way the arguments is said to be strong; if not, it is weak. Thus, a strong inductive argument is an argument such that if the premises are assumed true, it is improbable for the conclusion to be false. In such arguments, the conclusion follows probably from the premises. Conversely, a weak inductive argument is an argument such that if the premises are assumed true, it is probable for the conclusions to be false. In these arguments, the conclusion does not follow probably from the premises, even though it is claimed to. Consider the following examples: Example-1: Therefore, probably all one hundred apples This barrel contains one hundred apples. are tasty. Eighty apples selected at random were Example-2: found tasty. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 79 This barrel contains one hundred apples. Three apples selected at random were found tasty. Therefore, probably all one hundred apples are tasty. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 80 The first example is strong argument, because the conclusion actually follows probably from the premises. The second example is weak argument, because the conclusion does not actually follow probably from the premises, even though it is claimed to. The procedure for testing the strength of inductive arguments runs parallel to the procedure for deduction. Strength and Truth Value Just as what happened from definitions and examples of valid and invalid arguments earlier, two immediate conclusions follow from the above definitions and examples of strong and weak arguments. The first is that, unlike the validity and invalidity of deductive arguments, the strength and weakness of inductive arguments admit certain form of degrees. To be considered strong, an inductive argument must have a conclusion that is more probable than improbable. In inductive arguments, there is no absolutely strong nor absolutely weak argument. For instance, the first is not absolutely weak nor the second absolutely strong. Both arguments would be strengthened or weakened by the random selection of a larger or smaller sample. The incorporation of additional premises into inductive arguments will also generally tend to strength or weaken it. For example, if the premise ―one un-tasty apple that had been found earlier was removed‖ were added to the second argument, the argument would presumably be weakened. The second consequence is that, as validity and invalidity, strength and weakness are only indirectly related to the truth values of their premises. The central question in determining strength or weakness is whether the conclusion would probably true if the premises are assumed true. For an argument to be strong it is not necessary that either the premises or the conclusions be true, but merely that if the premises assumed true, it is improbable for the conclusion be false. That is, we do not have to know whether the premise of an argument is actually true in order to determine its strength (strong or weak). To test an argument for strength, what we need to do is to assume the premise true and then to see whether the conclusion follows more/less probably from the premise. Thus, the strength or weakness of an inductive argument results not from the actual truth or falsity of the premises and conclusion, but from the probabilistic support the premises give to the conclusion. By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 81 We have said earlier that there are four possibilities with respect to the truth or falsity of the premises and conclusion of a given argument: True premises and True conclusion, True premises and False conclusion, False premises and True conclusion, and False premises and False conclusion. These possibilities work in inductive arguments as well. Note that all of the above possibilities, except the second case (true premises and false conclusion), allow for both strong and weak arguments. That is, the second case does not allow for strong arguments. As we have just seen, any argument having this combination is necessarily weak. In general, the basic idea of evaluating inductive argument, strength is not something that is determined by the actual truth or falsity of the premises and conclusion, but by the relationship between premises and conclusion. Nevertheless, there is one arrangement of truth and falsity in the premises and conclusion that does determine the issue of strength. Thus, any inductive argument having actually true premises and an actually false conclusion is weak. The relationship between the strength of an inductive argument and the truth and falsity of its premises and conclusions summarized as follows. Table 1.2: Premises Conclusion Strength True True Strong/Weak True False Weak False True Strong/Weak False False Strong/Weak Induction and Cogency We said earlier that the evaluation of every argument centers on the evaluation of two claims: the inferential claim and factual claim of the argument. We have also said that we will always test the inferential claim first, and only if the premises do support the conclusion will we test the factual claim By: Teklay G. (AkU), Adane T. (MU), and Zelalem M. (HMU) 82 (that is, the claim that the premises present genuine evidence, or are true). Now that we have tested the inferential claims of inductive arguments, it is time to proceed to the next step: evaluating the factual claims of inductive arguments. Depending on their actual ability, (assuming that they already have actually accomplished their inferential claims by being strong), to accomplish their factual claims, inductive arguments can be either cogent or uncogent. A cogent argument is an inductive argument that is strong and has all true premises. Both conditions must be met for an argument to be cogent, and if either is missing the argument is uncogent. An inductive argument that does not actually accomplish its inferential claim, (that is not strong), cannot be cogent, regardless of the truth values of its premises. Such an inductive argument is uncogent, by definition. Thus, an uncogent argument is an inductive argument that is either strong with one or more false premises, or weak, or both. Because the conclusion of a cogent argument is genuinely supported by true premises, it follows that the conclusion of every cogent argument is probably true. A cogent argument is the inductive analogue of a sound deductive argument and is what is meant by a ‗‗good‘‘ inductive argument without qualification. Cogent Argument = A strong argument + All true premises There is a difference, however, between

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