PHL 152 Introduction to Logic II Course Guide PDF

COURSE GUIDE PHL 152 INTRODUCTION TO LOGIC II Course Team Prof. Ayodele Fadahunsi (Course Writer )-FUG Prof. Abdul Ganiyu A. Bello (Rtd) (Course Editor) Reprocessed by: Dr. Elochukwu Afoka NOUN NATIONAL OPEN UNIVERSITY OF NIGERIA PHL 152...

COURSE GUIDE PHL 152 INTRODUCTION TO LOGIC II Course Team Prof. Ayodele Fadahunsi (Course Writer )-FUG Prof. Abdul Ganiyu A. Bello (Rtd) (Course Editor) Reprocessed by: Dr. Elochukwu Afoka NOUN NATIONAL OPEN UNIVERSITY OF NIGERIA PHL 152 COURSE GUIDE © 2024 by NOUN Press National Open University of Nigeria Headquarters University Village Plot 91, Cadastral Zone, Nnamdi Azikiwe Expressway Jabi, Abuja Lagos Office 14/16 Ahmadu Bello Way Victoria Island, Lagos e-mail: [email protected] URL: www.nouedu.net All rights reserved. No part of this book may be reproduced, in any form or by any means, without permission in writing from the publisher. First Printed 2014, Reprint 2023, 2024 ISBN: 978-978-058 ii PHL 152 COURSE GUIDE CONTENTS Introduction ………………………………………….. iv Course Objectives ……………………………………. iv Working Through the Course ………………………... v Study Units …………………………………………... v References and Books for Further Reading ………….. vi iii PHL 152 COURSE GUIDE INTRODUCTION Welcome to PHL 152: Introduction to Logic II PHL 152 is a three- credit unit course with a minimum duration of one semester. It is a compulsory course for Philosophy Major (degree) students in the university. The course is a continuation of PHL 105. It studies the nature of truth and validity; induction and analogy; the nature of fallacies and psychological pitfalls in thinking; the modern scientific method of inquiry concerning Mill‘s method, etc. In this course, Material, effort is made to be as simple as possible in the writing and presentation of this study material to lead readers to effective grasping of its contents. The attempt to simplify the texts is with the realization that logic as a subject is not taught at the secondary school level. This means that the university beginners are just coming in close contact with it. Thus it becomes imperative to sectionalise the course outline into modules and units. Each module comprises several planned units under which pedagogy takes place. However, what is practically impossible is to avoid the technical nature of the subject. The language of the subject is technical and it cannot be otherwise. So, to some people who have a phobia for high web technicalities or calculation, logic is to such people a seemingly difficult enterprise. A conscious effort is therefore made to avoid the use of strictly mathematical jargon. Even though logic is very much akin to mathematics its subject-matter can be understood without any strong background in mathematics. Readers are therefore enjoined to go through this study material without any bias of the mind. It is lucidly written with local examples and clear illustrations. The aim is to equip students with logical skills that will enhance their reasoning ability. COURSE OBJECTIVES By the end of the course you will be able to: Learn about the history of logic. Acquire knowledge of laws of thought Explain the importance of logic. Explain the meaning of fallacy and types of fallacies. Differentiate between Formal and Informal Fallacies. Know what a logical puzzle is. Explain Categorical Syllogism. iv PHL 152 COURSE GUIDE Determine the validity and invalidity of Categorical Syllogism. Understand a rational proposition. Discuss the concept of ‗Definition ‘. Explain types of definitions and their values Explain the rules for definitions by Genus and Difference WORKING THROUGH THE COURSE To complete this course of study successfully, you are expected to read the study units, do all the assignments, open the links and read, participate in discussion forums, read the recommended books and other materials provided, prepare your portfolios, and participate in the online facilitation. Each study unit has an introduction, intended learning outcomes, the main content, a conclusion, a summary, and references/further readings. The introduction will tell you the expectations in the study unit. Read and note the intended learning outcomes (ILOs). The intended learning outcomes tell you what you should be able to do after each study unit. So, you can evaluate your learning at the end of each unit to ensure you have achieved the intended learning outcomes. You may wish to either print or download the text and save it on your computer. The conclusion gives you the theme of the knowledge you are taking away from the unit. Unit summaries are presented in downloadable audio and videos. There are two main forms of assessment—the formative and the summative. The formative assessment will help you monitor your learning. This is presented as in-text questions, discussion forums, and self-Assessment Exercises. The summative assessments would be used by the university to evaluate your academic performance. This will be given as a Computer Test (CBT) which serves as a continuous assessment and final examination. A minimum of two or a maximum of three computer-based tests will be given with only one final examination at the end of the semester. You are required to take all the computer- based tests and the final examination. STUDY UNITS There are 18 study units in this course divided into Four modules. The modules and units are presented as follows:- Module 1 Introduction to logic Unit 1 Meaning and Nature of logic Unit 2 A Brief History of logic Unit 3 Laws of Thought Unit 4 Meaning and Nature of Arguments Unit 5 Importance of Logic v PHL 152 COURSE GUIDE Module 2 Unit 1 The Meaning and Types of Arguments Unit 2 Structure of Arguments Unit 3 Informal Fallacies Unit 4 Informal Fallacies (Fallacies of Ambiguity) Unit 5 Informal Fallacies (Fallacies of Presumption) Unit 6 Exercise in Reason (Logical Puzzles) Module 3 Unit 1 Categorical Propositions Unit 2 Immediate Inference Unit 3 Categorical Syllogism Unit 4 Validity and Invalidity of Categorical Syllogism Unit 5 Rational Proposition Module 4 Unit 1 Disputes and Definitions Unit 2 Types of Definitions and their uses Unit 3 Rules for definitions by GENUS and Difference REFERENCES AND BOOKS FOR FURTHER READING Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). vi PHL 152 COURSE GUIDE Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). Lemmon, E.J. Beginning Logic (Ontario: Thomas Nelson, 1965) Thomas, S.T. Practical Reasoning in Natural Language (New Jersey: Prentice Hall Inc., 1997) vii  MAIN COURSE CONTENTS Module 1 Introduction to Logic ………………………. 1 Unit 1 Meaning and Nature of logic ……………………… 1 Unit 2 A Brief History of logic…………………………. 6 Unit 3 Laws of Thought………………………………… 10 Unit 4 Meaning and Nature of Arguments ……………….. 15 Unit 5 Importance of Logic……………………………... 20 Module 2 Informal Logic ……………………………… 25 Unit 1 The Meaning and Types of Arguments …………. 25 Unit 2 Structure of Arguments …………………………. 35 Unit 3 Informal Fallacies ………………………………. 44 Unit 4 Informal Fallacies (Fallacies of Ambiguity) ……. 53 Unit 5 Informal Fallacies (Fallacies of Presumption) …... 60 Unit 6 Exercise in Reason (Logical Puzzles) …………... 67 Module 3 Formal Logic ………………………………… 79 Unit 1 Categorical Propositions …………………………. 79 Unit 2 Immediate Inference ……………………………... 86 Unit 3 Categorical Syllogism ……………………………. 93 Unit 4 Validity and Invalidity of Categorical Syllogism …. 98 Unit 5 Rational Proposition …………………………….... 104 Module 4 Formal Logic …………………………………. 114 Unit 1 Disputes and Definitions………………………….. 114 Unit 2 Types of Definitions and their uses……………….. 120 Unit 3 Rules for definitions by GENUS and Difference…. 127 PHL 152 MODULE 1 MODULE 1 INTRODUCTION TO LOGIC Unit 1 Meaning and Nature of logic Unit 2 A Brief History of logic Unit 3 Laws of Thought Unit 4 Meaning and Nature of Arguments Unit 5 Importance of Logic Unit 1 Meaning and Subject Matter of Logic Unit Structure 1.1 Introduction 1.2 Learning Outcomes 1.3 Meaning and Nature of Logic 1.4 Types of Logic 1.5 Summary 1.6 References/Further Reading/Web Resources 1.7 Possible Answer to Self-Assessment Exercise 1.1 Introduction This introductory course in logic is aimed at exposing the student- philosopher to the world of logical thinking and equipping him/her with the tools s/he would need in life. It would attempt to define logic, explain its nature, discuss its types, delineate its history, and treat some of the key terms that have been the centerpiece of logical reasoning from antiquity. The three laws of thought would also be the focus here. Afterwards, emphasis would be placed on the relevance of logic, also known as the science of argumentation. In all, efforts would be made to explain the meaning, nature, and types of arguments, including the value and importance of logic in our everyday activities. 1.2 Learning Outcomes By the end of this unit, you will be able to:  explain the meaning and nature of logic;  discuss the types of logic;  distinguish between the types of logic that you have studied. 1 PHL 152 INTRODUCTION TO LOGIC II 1.3 The Meaning, Nature, and Types of Logic What is Logic? Logic is the branch of philosophy that investigates the art and science of reasoning. All the departments in the university employ logic in one way or the other. This is because logic includes all the laws guiding the various disciplines and areas of human inquiry. Logic never excludes any of the laws in the sciences, arts, or humanities. These laws guide human thought and reasoning in everyday life. Logic in this sense is reducible to the commonplace logic of the marketplace, which buyers and sellers of different goods and services deploy in entering into a deal or transacting a business. It includes the linguistic manipulation of the many men and women walking into the theatre to watch a dramatic show or a musical performance. It does not disregard the logic of the banking and insurance companies, the logic of the hospitals, clinics, and health centers. It does not undervalue the logic of all socio-politico- economic activities. It does not turn the logic of the court room into the logic of arguing implausibly or unreasonably. We cannot forget the logic behind the different religions in the world. Logic has not been an exclusive term and a core branch of philosophy. It is, however, not only the body or set of principles or ideas guiding a system of thought or idea. It is not only, as Francis Offor (2010: 3) describes, ―the principles guiding the operation of a mechanism.‖ A system, a school of thought, a mechanism, a person, or a gadget is ―guided by certain principles which can be referred to as the inner ‗logic‘ of that mechanism.‖ This idea of inner logic does not fully capture the philosophical definition or technical sense of logic as defined in philosophy. Basically, in philosophy logic as the laws of human thought is established on three basic laws of thought. This would soon be explained, as the first point of concern should be defining the nature of logic from the philosophical sense. As one of the core branches of philosophy, Logic can be defined as the science of distinguishing good reasoning from bad reasoning. It is ―the study of the basic principles, techniques, or methods for evaluating arguments (Offor 2010: 3). The distinction of arguments into valid and invalid forms, sound and unsound, deductive and inductive, has been the preoccupation of logicians for centuries. The Logic of Aristotle, the student of Plato and founder of the Lyceum, is seen as the earliest in the history of the science of inference. The Fregean notions of quantifiers, variables, and functions, and his evaluations of logic as a system of abstract mathematical system made the German logician, Gottlob Frege, the Father of Modern Logic. 2  PHL 152 MODULE 1 1.4 Types of Logic Logic is divided into two broad types which are informal and formal logic. 1. Informal Logic: This is the type of logic that deals with the analysis and evaluation of good and bad reasoning in everyday life. It probes the meaning and nature of argument in ordinary discourse and evaluates the informal fallacies of relevance, ambiguity, presumption, and evidence. Logical puzzles are also discussed as aspects of informal logic. 2. Formal Logic: This is the type of logic that is primarily concerned with the analysis and evaluation of the structures of statements and arguments in natural and artificial languages. While formal arguments in natural language include Categorical Syllogisms and Relational Arguments, formal statements and arguments in artificial language are part and parcel of Symbolic Logic. Formal errors in reasoning are called formal fallacies. 3. Other types of logic aside from the two, i.e. Formal logic and Informal logic that are commonly known are Boolean logic, Mathematical logic, Dialectical logic, etc. Self-Assessment Exercise 1 1. ____________________________ is the father of modern Logic. 2. _______________________ is the type of logic that is primarily concerned with the analysis and evaluation of the structures of statements and arguments in natural and artificial languages. 3. What do you understand to be informal Logic? Conclusion Logic has not been an exclusive term and a core branch of philosophy. It is, however, not only the body or set of principles or ideas guiding a system of thought or idea. 1.5 Summary In this unit, you have studied logic as a branch of philosophy that investigates the art and science of reasoning. It is one of the core branches of philosophy, defined as the science of distinguishing good reasoning from bad reasoning. 3 PHL 152 INTRODUCTION TO LOGIC II 1.6 References/Further Reading/Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). Lemmon, E.J. Beginning Logic (Ontario: Thomas Nelson, 1965) Thomas, S.T. Practical Reasoning in Natural Language (New Jersey: Prentice Hall Inc., 1997) 4 PHL 152 MODULE 1 1.7 Possible Answer to Self-Assessment Exercise 1 1. Gottlob Frege 2. Formal Logic 3. It is a Logic that deals with the analysis and evaluation of good and bad reasoning in everyday life. It probes the meaning and nature of argument in ordinary discourse and evaluates the informal fallacies of relevance, ambiguity, presumption, and evidence 5 PHL 152 INTRODUCTION TO LOGIC II UNIT 2 A BRIEF HISTORY OF LOGIC Unit Structure 2.1 Introduction 2.2 Learning Outcomes 2.3 A Brief History of Logic 2.4 Summary 2.5 References/Further Reading/Web Resources 2.6 Possible Answer to Self-Assessment Exercise 2.1 Introduction This unit introduces you to a short history of logic. You will study the history of logic from the Pre-Socratic, Medieval era to t h e Modern age of Francis Bacon‘s logic of inductive reasoning, Peirce theorem of propositional calculus, and many others. 2.2 Learning Outcomes By the end of this unit, you will be able to:  narrate the history of logical inquiry  distinguish the ages of the history of logic. 2.3 A brief history of logic Outline the history of logic. The science of correct and incorrect reasoning is traced back to the Pre- Socratic era when the atomists differentiated the quantitative qualities of atoms from the qualitative qualities. The Pythagorean mathematical model has some affinities with Logic but the beginning of classical logic is associated with the logical works of Aristotle namely Prior Analytics, Posterior Analytics, Categories, Interpretation, Sophistical Refutations, and Topics where we can delineate his categorical syllogism. Aristotle is regarded as the Father of Classical Logic. The most important contributions to Logic after Aristotle were the detailed and original logical inputs of the Stoics which were about the logic of propositions that foregrounded modern propositional logic (Lawhead 2002: 94). 6  PHL 152 MODULE 1 In the medieval era, the French philosopher, Roscelin de Compiègne, was known as a teacher of logic. William of Ockham, an English philosopher who wrote the Summa Logicae (Sum of Logic) argued that logic could only give us the forms of propositions we assert about reality but it cannot explain reality. The contributions of George Bull, the English mathematician culminated into what we refer to as the Boolean logic which shares some affinity with Boolean algebra. Bacon‘s inductivism, Mill‘s inductive principles, Lebniz‘s search for a universal, logically perfect language, Peirce‘s theorem of the propositional calculus, Russell‘s logical atomism, G. E. Moore‘s paradox, Goodman‘s paradox, Hempel‘s paradox, Popper‘s hypothetico- deductivism and the logical works of the logical positivists are references for us to interact with and come about a philosophical perspective which takes logic as crucial for analyses and evaluations. Self-Assignment Exercise 2 1. The beginning of classical logic is associated with the logical works of who? 2. The logic of propositions that foregrounded modern propositional logic was the original input of the ____________________________ to Logic. 3. The science of correct and incorrect reasoning is traced back to the Pre- Socratic era when the atomists differentiated the quantitative qualities of atoms from____________________ Conclusion The history of logic present to us the various stages of the development of philosophical inquiries. Through it, we can notice the different types of logic that were developed by various philosophers 2.4 Summary The history of logic is an age-long history. Logic grew along with the various schools of thought in philosophy and has remained the tool by which philosophers carry out their activities. 7 PHL 152 INTRODUCTION TO LOGIC II 2.5 References/Further Reading/Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). 8 PHL 152 MODULE 1 2.6 Possible Answer to Self-Assessment Exercise 1. Aristotle 2. Stoics 3. Qualitative qualities 9 PHL 152 INTRODUCTION TO LOGIC II UNIT 3 THE LAWS OF THOUGHT Unit Structure 3.1 Introduction 3.2 Intended Learning Outcomes 3.3 Laws of thought 3.3.1 The Law of Identity 3.3.2 The Law of Excluded Middle 3.3.3 The Law of Non-Contradiction 3.4 Summary 3.5 References/Further Reading/Web Resources 3.6 Possible Answer to Self-Assessment Exercise 3.1 Introduction In this unit, you shall be introduced to the various laws of thought guiding the different areas of knowledge. These are the Law of identity, The Law of Excluded Middle, and the Law of Non- Contradiction. 3.2 Intended Learning Outcomes By the end of this unit, you will be able to;  explain what the laws of thought are  discuss the law, of identity: the law of excluded middle and the law of non-  contradiction  give relevant examples of each of the laws of thought studied 3.3 The Laws of Thought List and explain the laws of thought. The history of human inquiry is the history of humankind‘s quest for meaning. There cannot be any meaning-creating action without an idea, a principle, or a thought. All the ideas, concepts, precepts, notions, principles, and rules of the different areas of knowledge must not be contrary to any of the three laws of thought, which are also known as the primary laws of thought. There is no discipline whose basic, underlying principles are opposed to the primary laws of thought. An explanation 10 PHL 152 MODULE 1 cannot be given in defense of a branch of learning whose system of rules is not according to the basic laws serving as the basis of all knowledge. These three laws are listed below: 1. The Law of Identity 2. The Law of Excluded Middle 3. The Law of Non-Contradiction These fundamental laws must be understood in connection to all the forms of inquiry in the world operating according to a two-value logic system. We must further know the logical forms of the three laws for easy correlation of ideas. 3.3.1 The Law of Identity This states that if any statement is true, then it is true. A true statement is. This implies, for example, that, something cannot be in existence and not in existence at the same time. Being cannot misidentify itself. Being is identical to itself. The Law of Identity can be schematically represented as P is P. 3.3.2 The Law of Excluded Middle This simply states that a statement is either true or false. It also means that a statement cannot be both true and false. The value of a statement cannot be indifferent to any quality. There cannot be a true and false answer to the same question with the same signification. A statement or an answer is either affirmative or negative. It is either an affirmation or a negation. 3.3.3 The Law of Contradiction or Non-Contradiction: This states that a statement cannot be both true and false at the same time. What this self- contradictory statement implies is that every statement that is both true and false is false. A mango tree cannot be a cashew tree. It is either a mango tree or a cashew tree and not both. Human experience has not given us an instance. To say that a tree can bear mango fruits as well as cashew fruits is to think or imagine such a possibility outside the confines of human experience. 11  PHL 152 INTRODUCTION TO LOGIC II Self-Assessment Exercise 3 1. _________________________ law of thought states that something cannot be in existence and not in existence at the same time. 2. __________________ states that a statement cannot be both true and false at the same time. 3. All the ideas, concepts, precepts, notions, principles, and rules of the different areas of knowledge must not be contrary to any of the three laws of thought, which are also known as the primary laws of thought. TRUE/FALSE Conclusion The underlying idea is that all disciplines are not opposed to the primary laws of thought. 3.4 Summary The study of the laws of thought i.e. Law of identity, Law of Excluded middle, and Law of Non- Contradiction in this unit shows that every discipline exhibits principles that obey these laws. These fundamental laws must be understood in connection to all the forms of inquiry in the world operating according to a two-value logic system. 3.5 References/Further Reading/Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) 12 PHL 152 MODULE 1 Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). Lemmon, E.J. Beginning Logic (Ontario: Thomas Nelson, 1965) Thomas, S.T. Practical Reasoning in Natural Language (New Jersey: Prentice Hall Inc., 1997) 13 PHL 152 INTRODUCTION TO LOGIC II 3.6 Possible Answer to Self-Assessment Exercise 1. The law of Identity 2. Law of Contradiction. 3. True 14 PHL 152 MODULE 1 UNIT 4 THE MEANING, NATURE AND NATURE OF ARGUMENT Unit Structure 4.1 Introduction 4.2 Learning Outcomes 4.3 Meaning and Nature of argument 4.4 Types of Logic 4.5 Summary 4.6 References/Further Reading 4.7 Possible Answer to Self-Assessment Exercise 4.1 Introduction In this unit, we shall discuss the meaning and nature of the argument. You shall also be introduced to the various types of argument i.e. Inductive and Deductive arguments. You shall also learn the distinctions between the two types of arguments that shall be studied. 4.2 Learning Outcomes By the end of this unit, you should be able to:  explain the term argument  discuss inductive and deductive types of argument in logic  distinguish between Inductive and Deductive argument 4.3 The meaning and nature of the argument What is an argument? The term argument is etymologically derived from a Latin word, ―argue” which means to prove or to make clear. It is a term that has occupied a central position in both professional and unprofessional parlances. It is the word used by the couple quarreling or fighting over who is to prepare supper. Imagine this conversation between a couple: ―I have a backlog of work in the office and though I am your wife, you should not dare touch me again the wife said. ―I would not only touch you. I would rather make you disfigured and unrecognizable by your boss if you do not consider changing your job.‖ 15 PHL 152 INTRODUCTION TO LOGIC II The husband sneezed and the next second was the minute of insults. Like the husband and wife insulting each other because of an evening meal which was supposed to be the time of the meeting, eating, drinking, and examining all the frowns and smiles of the day but has been turned into a moment of quarreling, the meaning of argument can be because of a minor error, a slip of the tongue or a slip of the pen. The science of argumentation goes beyond the popular connotation of quarreling, disagreeing, and fighting. An argument can simply be defined as a group or set of statements in which one, conclusion is inferred from other statements known as premises. An argument shows the structure or pattern of an inference. It is either a proof or a refutation. It is proof when it demonstrates the truth of a proposed conclusion from a group of premises. It is a refutation when it demonstrates the falsity of a proposed conclusion from a group of premises accepted as true. Although proofs and refutations can sometimes be discussed as types of argument, there are mainly two types of arguments. Before we explain the types of argument, we should note that an argument is an effort to state reasons why a statement should be accepted as true or rejected as false. In every argument, there are three elements which include the person making the argument/claim, a premise or a reason justifying the acceptance or rejection of the claim, and a conclusion of the claim. An argument is not about sentences but statements. While a sentence can be without any truth-value, a statement is a sentence that is either true or false. The link from the premises to the conclusion is the inference or logical connection between the premises and the conclusion. The conclusion and premises of a claim are oftentimes indicated through what are called conclusion and premise indicators. However, there is also the need to note that this is not always the case in the presentation of arguments or claims. In other words, an argument may still be obtainable even in the absence of such indicators, and this would be mainly discovered through drawing inferences from the statement or propositions. Conclusion indicators include consequently, it follows that, it implies that, hence, so, therefore, that’s why and this entails that. Premise indicators such as granted that, given, in as much as, because, since and this is true because among many others make us recognize the premises of a given argument. 4.3.1 Types of Argument List and explain the types of argument There are two main types of arguments namely deductive argument and inductive argument. These are forms of reasoning we often make use of 16  PHL 152 MODULE 1 in the different areas of human thought. A deductive argument is an argument in which the premises do not only support but also guarantee the conclusion. Put differently, the conclusion of a deductive argument is directly inferred from its premises. If the conclusion of an argument is directly inferred from its premises, it follows, therefore, that there can be nothing contained in the conclusion, which is not already contained in the premises. On the order hand, an argument is said to be inductive if its premise(s) only support but do not guarantee its conclusion. This kind of argument does not claim that their premises, even if true, support their conclusions with certainty. Inductive arguments make weaker but important claims that their premises support their conclusion with probability, which always falls short of certainty. It is also noted in the inductive mode of reasoning, that the conclusion logically implies an item of information not necessarily implied by the premises; ―and that which can be confirmed or refuted only based on evidence drawn from sense experience (Ade-Ali, 2000:265) A tabular presentation as seen below would further make this distinction between a deductive and an inductive argument clearer: 4.3.2 Differences Between a Deductive and an Inductive Argument S/No Deductive Argument Inductive Argument 1. A deductive argument can either An inductive argument can either be validor invalid. be more or less probable. 2. If the premises provide Premises cannot provide conclusive conclusive support for the truth support for the conclusion and, hence of the conclusion, then it is said to cannot be said to be valid. be valid. 3. The premises can't be true and the The premises can be true, and the conclusion to be false, if it is conclusion to be false. valid. 4. A deductive argument is analytic. An inductive argument is empirical. Self-Assessment Exercise 4 1. Argument is etymologically derived from ____________________ 2. __________________ is a type of argument that can either be valid or invalid 3. List and explain the two types of argument. 17 PHL 152 INTRODUCTION TO LOGIC II Conclusion Not every discussion can be referred to as an argument. All forms of arguments must have premises and conclusion. 4.5 Summary In this unit, you have been introduced to the meaning and nature of argument. Two types of argument were discussed, which are the Inductive argument and the Deductive argument. While all inductive arguments are considered to be invalid and unsound, some deductive arguments are valid and sound. 4.6 References/Further Reading/Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). 18 PHL 152 MODULE 1 4.8 Possible Answer to Self-Assessment Exercise 4 1. Argue 2. Deductive argument 3. Deductive and inductive argument. A deductive argument is an argument in which the premises do not only support but also guarantee the conclusion. Put differently, the conclusion of a deductive argument is directly inferred from its premises. An argument is said to be inductive if its premise(s) only support but do not guarantee its conclusion. This kind of argument does not claim that their premises, even if true, support their conclusions with certainty. Inductive arguments make weaker but important claims that their premises support their conclusion with probability, which always falls short of certainty. 19 PHL 152 INTRODUCTION TO LOGIC II UNIT 5 THE IMPORTANCE OF LOGIC Unit Structure 5.1 Introduction 5.2 Learning Outcomes 5.3 The importance of logic to character development 5.4 The importance of logic to discovery and rediscovery of truth 5.5 The importance of logic to the resolution of disputes 5.6 The importance of logic to the development of rational conviction 5.7 The importance of logic to behavioral inspiration and motivation 5.8 Summary 5.9 References/Further Reading 5.10 Possible Answer to Self-Assessment Exercise 5.1 Introduction Logic is the branch of philosophy which all other branches of philosophy and indeed all other departments of knowledge production, application, and consumption cannot be divorced from to create meaning in life. The appreciation of logic may not be the topic of discussion in the church, in the mosque, in the shrine, in the marketplace, in the hotel, in the the town hall or even in the court of law where logic is applied in the prosecution and defense of accused persons. Some of the importance of logic in life are outlined below: 5.2 Learning Outcomes By the end of this unit, students should be able to: Explain the relevance of logic to human beings and their environment 5.3 Character Development What is the importance of argument? The formulation of arguments may not instantly make any man or woman see how the formation of a moral character follows the laws of logic. The way we feel, think, speak, and act distinguishes the logical from the illogical, the rational from the irrational, and the good from the bad. It is not always the case that we are as our thoughts, words, and actions present us to the world but living against good reasoning and 20 PHL 152 MODULE 1 appearing to be reasonable disconnects the person from himself/herself. There is no way an individual‘s thoughts, words, and actions would reveal the good when the person is indeed bad. If there is no co- relationship between the feelings, thoughts, words, and actions of a person, then we should be diagnosing a self-alienated personality, going about his or her activities with the fear of the truth that would ultimately be seen lying at the bottom of the well. The morally upright person may not know the categories of thought but the life of such a person would be according to the logic of morality which cannot be contradicted by the science of logic. 5.3.1 The Discovery and Rediscovery of Truth The knowledge of the correct and incorrect ways of reasoning helps the seeker of truth to discover and rediscover the truth on the road of life. Truth and falsehood are terms we can relate to on a daily basis. There is hardly any day when a lie or a truth is not said or heard. Grasping the tools of logic would lead to the truth not merely according to the logical structure or the mere formulation of arguments but according to the desire to attain a life of order, happy ending, and meaning. 5.3.2 The Resolution of Disputes The tools of logic have been used in different law courts and tribunals all over the world to resolve issues in society which range from family to office matters, religious to political cases, issues concerning property acquisition, and other sundry problems plaguing the human society. The court of law has been the best application of logic to argue cases not necessarily to win against the opponent but to bring about justice which cannot be achieved in the absence of truth. 5.3.3 The Development of Rational Conviction The idea or belief we live by invites or attracts critics who are not always keen on knowing why an idea should guide us. What is this thing called idea or belief? We go to the Church without conviction. We go to the mosque without conviction. We go into different relationships without conviction and end up with self-deceit, hypocrisy, bad faith, and inauthenticity as byproducts of our reckless convictions. Logic makes us rationally convinced of what idea we cling tenaciously to and whether or not we live with people having a mutual idea, we would not easily be dissuaded or discouraged or persuaded only if the truth is what we are discovering and what we have always agreed to have been a lie. 21  PHL 152 INTRODUCTION TO LOGIC II 5.3.4 Behavioral Inspiration and Motivation As we distinguish good from bad arguments, explaining and discouraging ourselves from wrong forms of thinking, we are inspired and motivated to live the good life. Self-Assessment Exercise 5 1. List the five importance of Logic. 2. Logic brings about a good life. TRUE/FALSE Conclusion The relevance of logic may not be the topic of discussion among men, disciplines, in the town hall, or even in the court of law where logic is applied in the prosecution and defense of accused persons. But is importance cannot be undermined in any form. 5.6 Summary In this lecture, you have been introduced briefly to the nature and meaning of logic, the three laws of thought, the nature, and types of argument, as well as the distinction between deductive and inductive arguments, and the value or relevance of logic in everyday life and human thought. This brief introduction is mainly to serve as an eye- opener to the world of logic, especially as conceived in the philosophical enterprise. In the following modules, you would be taken through detailed explanations, illustrations, and samples of deductive and inductive, valid and invalid, sound and unsound arguments, as well as the nature of formal and informal logic, meaning, and definitions. 5.7 References/Further Reading/ Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to CriticalThinking (Ibadan: Hope Publications, 2006). 22 PHL 152 MODULE 1 5.8 Possible Answer to Self-Assessment Exercise 5 1. Character Development, Dispute Resolution, Behavioral Motivation, and inspiration, Development of Rational Conviction, and discovery and Rediscovery of Truth 2. True. 23 PHL 152 INTRODUCTION TO LOGIC II Tutor-Marked Assignment 1. Define logic. 2. List he types of logic known to you. 3. Outline the history of logic. With relevant examples explain 4. The law of identity 5. The law of Excluded Middle 6. The law of Non-Contradiction 7. What is argument? 8. What is an argument? 9. List and explain the two types of argument. 10. Mention 2 differences between deductive and inductive arguments. 11. List 2 premise indicators and 2 conclusion indicators. 12. What is Logic? 13. How can you differentiate informal logic from formal logic? 14. Who is the Father of Classical Logic? 15. Who is the Father of Modern Logic? 16. List 4 other logicians you know. 17. Would you want to become a logician? Defend your answer. 18. State the usefulness of logic. 24 PHL 152 MODULE 2 MODULE 2 INFORMAL LOGIC Unit 1 The Meaning and Types of Arguments Unit 2 Structure of Arguments Unit 3 Informal Fallacies Unit 4 Informal Fallacies (Fallacies of Ambiguity) Unit 5 Informal Fallacies (Fallacies of Presumption) Unit 6 Exercise in Reason (Logical Puzzles) Unit 1 The Meaning and Types of Argument Unit Structure 1.1 Introduction 1.2 Learning Outcomes 1.3 Propositions 1.4 Arguments 1.5 Recognizing Arguments 1.6 Summary 1.7 References/Further Reading 1.8 Possible Answer to Self-Assessment Exercise 1.1 Introduction In this unit, we shall begin by looking at one basic concept concerning arguments, that is, proposition. After that, we would look at arguments. This opening lecture is quite important because our understanding of this concept will aid our grasping the substance of this lecture. We shall also be looking at how to analyse arguments, premise-indicators, and conclusion-indicators. 1.2 Learning Outcomes By the end of this unit, you should be able to:  understand the meaning of a proposition and distinguish between simple and compound propositions.  define what an argument is. 25 PHL 152 INTRODUCTION TO LOGIC II 1.3 Propositions What is a proposition? A proposition can be used to refer to the content of a meaningful declarative sentence or the pattern of symbols, marks, or sounds that make up a meaningful declarative sentence. It ―asserts that something is (or is not) the case; any proposition may be affirmed or denied‖ (Copi & Cohen 2006: 2). A proposition has the quality or property of being true or false, implying that every proposition must be either true or false. This is why propositions are sometimes referred to as ―truthbearers‖. Truth and falsity therefore apply always to propositions. Copi & Cohen distinguish between propositions and sentences. They point out that sentences are how propositions are asserted. Put differently, ―Two different sentences, consisting of different words differently arranged, may have the same meaning and be used to assert the same proposition‖ (Copi & Cohen 2006: 2). For instance, the following are two different sentences that make the same assertion: ―Muhammadu Buhari won the 2015 Presidential Election in Nigeria‖ and ―The 2015 Presidential Election was won by Muhammadu Buhari.‖ We must add here that the terms ―proposition‖ and ―statement have been used interchangeably by some logicians. Therefore, the term ―statement, though not an exact synonym of proposition, ―is used in logic in much the same sense. Some logicians prefer statements to propositions, although the latter has been more common in the history of logic‖ (Copi & Cohen 2006: 2). There are simple as well as compound propositions. A simple proposition makes only one assertion, while a compound proposition contains two or more simple propositions. In other words, you assert more than one proposition in a compound proposition. For example: i. The largest country in the world is the third most populous country in the world. ii. The man who won the 2011 Presidential Election is the President of Nigeria. iii. By the 1830s white men were the dominant race in the Hunter Valley. Most of the prime land along the main river frontages had been taken up for crops and cattle and settlers were moving into the back country north and west of the Hunter. After 1830 most resistance by the Kooris was passive, although there were spasmodic outbreaks of violence. Nevertheless, the two races could not live completely apart and growing contact was inevitable (cited in Copi & Cohen 2006). iv. Turning local government areas into development areas will 26 PHL 152 MODULE 2 maximise growth. We say this because turning local government areas into development areas will depoliticise development, as suspicions of neglect due to fears of ethnic domination in various states will diminish, and support for the party at the helm of affairs at the state capital or center will also cease to be the basis for the provision of amenities in local government areas. (Adapted from African Guardian). Examples (i) and (ii) are simple propositions, while (iii) and (iv) are examples of compound propositions. 1.3.1 Arguments According to Copi & Cohen (2006: 4): Propositions are the building blocks of which arguments are made. When we reach or affirm one proposition based on other propositions, we say that an inference has been drawn. Inference is a process that may tie a cluster of propositions together. Some inferences are warranted or correct, others are not. To determine whether an inference is correct, the logician examines the propositions with which the process begins and ends, and the relations between those propositions. This cluster of propositions constitutes an argument. Arguments are the chief concern of logic. The term ‗argument‘ can have a dual meaning. In ordinary discourse, it connotes a quarrel or disagreement, whereas in logic – that is, in the technical sense – an argument is a sequence of statements,‗declarative sentences‘ or propositions, in which one part known as the conclusion is claimed to follow from the others called the premises. In clear terms, therefore, an argument is any group of propositions which one is claimed to follow from the others, which are regarded as providing support or grounds for the truth of that one. That means that an argument is not just a mere collection of statements. An argument has a structure that is defined by the terms ‗premises‘ and ‗conclusion‘ and the nature of the relationship between them. The conclusion of an argument is that proposition that is affirmed based on some other propositions, which serve as justification for the acceptance of the conclusion. These other propositions, which go by various names such as evidence, grounds, or reasons, are more technically called premises. In an argument, therefore, the premises are intended to provide sufficient grounds for the acceptance of the conclusion. For an argument to be present, ―there must be some structure within the cluster of propositions, a structure that captures or exhibits some inference. This structure we describe using the terms premise and conclusion (Copi & Cohen 2006: 4). Thus, the premise is a 27 PHL 152 INTRODUCTION TO LOGIC II proposition used in an argument to support some other proposition, while the conclusion is the proposition in an argument in which the other propositions (that is, the premises) support. Where there is no relationship whatsoever between the putative claim or conclusion and the reasons given for its acceptance, then there is no argument. An argument may have two sentences where the first sentence serves as the basis for accepting the other which is the conclusion. In other words, the premise and the conclusion may be stated separately, each in a separate sentence. For example: (i) Ole Farmer has not been convicted of the crime of murder. Therefore, any statement indicting him of the murder should be jettisoned as a mere insinuation. (ii) Okon is a politician who has recorded great success at the state level. Therefore, he will winthe presidential election in 2015. Sometimes, both the premise and the conclusion may be stated in the same sentence. For example: (i) Since it turns out that all humans are descended from a small number of African ancestors in our recent evolutionary past, believing in profound differences between the races is as ridiculous as believing in a flat earth (Copi & Cohen 2006: 4). (ii) Since it was clear that Daryll was not in London when her husband died, it would be wrong to bring her to court for questioning. (iii) Large numbers of people in this country have never had to deal with the criminal justice system, thus they are unaware of how it works and of the extraordinarily detrimental impact it has upon many people‘s lives. (iv) Human brains have the same kind of chemistry and cell receptors as rats regarding glucocorticoids, so, it seems possible that our response to being handled as infants is similar. In an argument with two separate sentences (one the premise and the other the conclusion), the statement of the conclusion may be stated first before the statement of its premise. For example: (i) Smoking in public places should be banned immediately. After all, passive smoking can cause cancer in non-smokers (Copi & Cohen 2006: 5). (ii) Corrupt politicians should be banned from holding public offices. (iii) After all, statistics have shown that corrupt politicians who hold 28 PHL 152 MODULE 2 public offices are responsible for our economic problem. It is also the case that, even when the premise and conclusion are united in one sentence, the conclusion of an argument may be stated first before its single premise. Let‘s take, for example, a statement made by Malcolm X in 1965: You can‘t separate peace from freedom because no one can be at peace unless he has freedom. The above examples of simple arguments remind us that, in some arguments, the premises of the argument are stated first and the conclusion last. In some others, the conclusion is either stated first or is sandwiched in-between different premises offered in its support. Just as we distinguished between simple and compound propositions, it must be stated that most arguments are more complicated than the ones we used as examples. In other words, ―some arguments contain compound propositions with their several components related intricately‖ (Copi & Cohen 2006: 5). This means that we have cases where an argument has two or more propositions (premises) supporting a proposition (conclusion). We must be warned however that some compound propositions may resemble arguments; to determine whether a group of propositions or statements is an argument or not, therefore, we should ensure that (1) an inference is drawn and (2) a conclusion should be claimed to be true. For example: Life likely evolved on countless other planets that scientists now believe exist in our galaxy because life very probably evolved on Mars during an early period in its history when it had an atmosphere and climate similar to Earth‘s (cited in Copi et al 2006). In the above argument, an inference is drawn and a conclusion is claimed to be true. The proposition ―that life very probably evolved on Mars during an early period in its history is asserted as a premise and the proposition ―that life likely evolved on countless other planets‖ is here claimed to follow from that premise and to be true. 1.3.2 Recognizing Arguments (i) An argument may have two sentences where the first sentence serves as the basis for accepting the other which is the conclusion. In other words, the premise and the conclusion may be stated separately, each in a separate sentence. (ii) Sometimes, both the premise and the conclusion may be stated in the same sentence. (iii) In an argument with two separate sentences (one the premise and the other the conclusion), the statement of the conclusion may be stated first before the statement of its premise. 29 PHL 152 INTRODUCTION TO LOGIC II (iv) It is also the case that, even when the premise and conclusion are united in one sentence, the conclusion of an argument may be stated first before its single premise. The inference from this is that, in some arguments, the premises of the argument are stated first and the conclusion last. In some others, the conclusion is either stated first or is sandwiched in-between different premises offered in its support. To arrange such arguments into their premises and conclusions, we use words and phrases that are referred to variously as conclusion-indicators and premise-indicators. The following is a list of some conclusion-indicators: Therefore, Hence, So, Accordingly, In consequence, Consequently, Proves that, As a result, Thus, For this reason, which points to the conclusion that, For these reasons, It follows that, I conclude that, Which shows that, Which means that, Which entails that, Which implies that, Which follows that, We may infer that. The following is a list of premise-indicators: Since, For, As, Because, Follows from, As shown by, In as much as, The reason is that, For the reason that, As indicated by, May be inferred from, May be derived from, May be deduced from, Because. Let us rely on these indicators to identify the premises and conclusions in the following arguments: (i) What science cannot know; mankind cannot know. Therefore, all knowledge comes from science. (ii) Abortion is evil not only to the victim but also to our sense of justice. Hence, it should be abolished. (iii) Since man is created first, man should be the master of all creatures (Offor 2012: 16). In (i) and (ii), the indicators ―therefore‖ and ―hence‖ help to identify the conclusions which affirm that ―... all knowledge comes from science and that abortion ―... should be abolished‖ respectively. In (iii), the indicator ―inasmuch as helps to identify the premise which gives support to the claim (conclusion) that―man should be the master of all creatures‖. It must be stated, however, that ―the words and phrases listed above may help to recognize the presence of an argument or identify its premises or conclusion, but such indicators do not necessarily appear. Sometimes it is just the meaning of the passage, or its setting, that indicates the presence of an argument (Copi & Cohen 2006: 28). Thus, if an argument does not have premise or conclusion indicators, we are required ―to identify the claim the person presenting the argument is trying to make. This is the conclusion of the argument, while the reasons given in support of such a claim are the premises of the argument (Offor 2012: 17). 30 PHL 152 MODULE 2 Sample Excises: (see Copi & Cohen 2006: 6 – 9) Identify the premises and conclusions in the following passages, each of which contains only one argument: (i) ―Untouchability‖ is abolished and its practice in any form is forbidden. The enforcement of any disability arising out of ―Untouchability‖ shall be an offence punishable in accordance with the law. Solution: Premise: ―Untouchability‖ is abolished and its practice in any form is forbidden. Conclusion: The enforcement of any disability arising out of ―Untouchability‖ shall be an offence punishable by the law. (ii) Because light moves at a finite speed, looking at objects that are millions of miles away is actually at the light that was emitted many years ago. Solution: Premise: Light moves at a finite speed Conclusion: Looking at objects that are millions of miles away is looking a light that was emitted many years ago. (iii) Because the education of parents directly impacts the ability of their children to succeed in school, it is an urgent necessity that this generation of Nigerian youth is properly educated. Solution: Premise: The education of parents directly impacts the ability of their children to succeed in school. Conclusion: It is an urgent necessity that this generation of Nigerian youth is properly educated. (iv) Unquestionably, no more important goal exists in medical research today than the development of an AIDS vaccine. Last year... AIDS, caused by HIV (Human Immunodeficiency Virus) was the infection disease that killed the most people around the world, and the epidemic is not abating. Solution: Premise I: In 1988 AIDS was the infectious disease that killed most people around the world. Premise II: The AIDS epidemic is not abating. Conclusion: Unquestionably, no more important goal exists in medical research todaythan the development of an AIDS vaccine. 31  PHL 152 INTRODUCTION TO LOGIC II Self-Assessment Exercise 1 1. _____________________ is referred a meaningful Declarative Statement. an argument is a sequence of statements, 2. ____________________________ is a sequence of statements or declarative sentences‘ or propositions, in which one part known as the conclusion is claimed to follow from the others called the premises. Conclusion Although, in logic, the term ―statement is not synonymous with ―proposition‖, however, it is used in much the same sense. Also, arguments in logic consist of two sentences. The first sentence serves as the basis for accepting the other, which is the conclusion. 1.4 Summary In this unit, we looked at the basic concepts that are most central to this course, Introduction to logic II, namely, logic, propositions, and arguments. We defined logic as the study of the methods and principles used to distinguish correct from incorrect reasoning. We gave an account of propositions and distinguished them from the sentences in which they may be expressed. We gave an account of the concept of an argument and defined an argument as a cluster of propositions of which one is the conclusion and the other(s) are premises offered in its support. Finally, in the lecture, we looked at ways of recognizing arguments through phrases and words we call conclusion indicators and premise- indicators. 1.5 References/Further Reading/Web Resources Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy(London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). 32 PHL 152 MODULE 2 Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). 33 PHL 152 INTRODUCTION TO LOGIC II Possible Answer to Self-Assessment Exercise 1 1. Proposition 2. Argument 34 PHL 152 MODULE 2 UNIT 2 THE STRUCTURE OF ARGUMENTS Unit Structure 2.1 Introduction 2.2 Learning Outcomes 2.3 Deductive and Inductive Arguments 2.4 Truth, Validity and Soundness 2.5 Summary 2.6 References/Further Reading 2.7 Possible Answer to Self-Assessment Exercise 2.1 Introduction In unit 1, we pointed out that a proposition may not necessarily qualify as an argument; to determine whether a group of propositions or statements is an argument or not, therefore, we should ensure that an inference is drawn, and a conclusion should be claimed to be true. But there are two different ways in which a conclusion of an argument may be supported by its premises, namely, (i) the premises may give total support to the conclusion of an argument and (ii) the premises may support the conclusion only with some degree of probability. This distinction informs why arguments are categorized into two: Deductive and Inductive. 2.2 Learning Outcomes By the end of this unit, you should be able to:  distinguish between deductive and inductive arguments.  give examples of both deductive and inductive arguments.  understand valid and invalid arguments.  know the relation that exists between truth and validity of an argument. 2.3 Deductive and Inductive Arguments What is the difference between deductive and inductive argument? Historically speaking, deductive reasoning can be traced back to the ancient Greek philosopher, Aristotle. Inductive reasoning, on the other 35 PHL 152 INTRODUCTION TO LOGIC II hand, was developed by the famous British philosopher, Francis Bacon and his successor, J.S. Mill. It is important to note that: A deductive argument claims that its conclusion is supported by its premises conclusively. An inductive argument, in contrast, does not make such a claim. Therefore, if we judge that in some passage a claim or conclusiveness is being made, we treat the argument as deductive; if we judge that such a claim is not being made, we treat it as inductive. Since every argument either makes this claim of conclusiveness (explicitly or implicitly) or does not make it, every argument is either deductive or inductive (Copi & Cohen 2006: 9). There are distinguishing features between deductive and inductive arguments. If we are confronted with an argument whose truth of its premises guarantees the truth of its conclusion, then that argument is said to involve a deductive inference. In other words, ―a deductive inference succeeds only if its premises provide such absolute and complete support for its conclusion that it would be utterly inconsistent to suppose that the premises are true but the conclusion false‖ (Offor 2012: 22). On the other hand, an argument is said to involve an inductive inference if it ―claims merely that the truth of its premises make it likely or probable that its conclusion is also true‖ (Ibid.) This means that in an inductive argument, the premises do not give total support to the conclusion but merely provide some grounds for the truth of their conclusions. The foregoing can be termed as the distinguishing features between deductive and inductive arguments. These features can be summarised thus: 1. In a deductive argument, the premises conclusively or logically imply the conclusion; in an inductive argument, the premises only provide some probable grounds for the acceptance of the conclusion. 2. If the premises of a deductive argument provide conclusive grounds for the truth of the conclusion, then the argument is said to be valid; inductive arguments cannot be valid but can be strengthened or weakened by additional premises. 3. If a deductive argument is valid, then it is impossible for its premises to be true and its conclusion false; it is possible for the conclusion of an inductive argument to be false even when the premises are true (Offor 2012: 23). Examples of deductive argument are: (i) All humans are mortal Aristotle is human Therefore, Aristotle is mortal. 36 PHL 152 MODULE 2 (ii) All humans are animals All animals are mortal Therefore, all humans are mortal. (iii) All Nigerians are Africans All Africans are coloured Therefore, all Nigerians are coloured. (iv) In order to study in the United Kingdom, you have to develop yourself in the field of philosophy, and in order to develop yourself in the field of philosophy, you have to read the works of Plato and Aristotle. Therefore, in order to study in the United Kingdom you have to read the works of Plato and Aristotle. Examples of an inductive argument are: (i) John is human and is mortal Peter is human and is mortal James is human and is mortal Therefore, all humans are mortal. (ii) Kennedy was an orator and was a good leader. Churchill was an orator and was a good leader. Babangida was an orator. Therefore, Babangida will be a good leader. (iii) The cows have kidneys and have lungs. All horses have kidneys and have lungs. All human beings have kidneys and have lungs. Therefore, all animals with kidneys have lungs. (iv) All politicians are criminals and will eventually die All soldiers are criminals and will eventually die Therefore, all men are criminals and will eventually die. 2.3.1 Truth, Validity and Soundness Earlier in this unit, we pointed out that, in deductive arguments, the premises provide conclusive grounds for the truth of the conclusion. A statement or proposition is said to be true if it expresses what really the case is and is false if it does not conform with the situation it expresses. More lucidly, truth is the attribute of a statement or proposition that asserts what really is the case. Therefore, when the premises provide conclusive or incontrovertible grounds for the truth of the conclusion, the argument is said to be valid. This shows that there is some connection between truth and validity of an argument. However, the term validity is applicable only to deductive arguments and to say that a deductive argument is valid is to say that it is not possible for its conclusion to be false if its premises are true. Thus, ―a deductive argument is valid when, if its premises are true, its conclusion must be true‖ (Copi & Cohen 2006: 9). But if the premises of a deductive 37 PHL 152 INTRODUCTION TO LOGIC II argument fail to guarantee the truth of its conclusion, the argument is said to be invalid. Here, it is instructive to show the contrast between truth and validity. If, for instance, I assert that Nigeria‘s premier university is situated in Ibadan, the capital of Oyo State, I assert what really is the case, what is true. If I had claimed that the premier university is in Abuja, my assertion would not be in accord with the real world; therefore, it would be false. It can be gleaned, therefore, that ―truth and falsity are attributes of individual propositions or statements; validity and invalidity are attributes of arguments‖ (Copi & Cohen 2006: 12). Copi & Cohen (2006: 12) explicate further on the relations between truth and validity by pointing out that: Just as the concept of validity cannot apply to single propositions, the concept of truth cannot apply to arguments. Of the several propositions in an argument, some (or all) may be true and some (or all) may be false. But the argument as a whole is neither true nor false. Propositions, which are statements about the world, may be true or false; deductive arguments, which consist of inferences from one set of propositions to other propositions, may be valid or invalid. With seven illustrative arguments, Copi & Cohen (2006: 13 – 14) show that there are many possible combinations of true and false premises and conclusions in both valid and invalid arguments, implying that (1) an argument may be valid even when its conclusion and one or more of its premises are false and (2) the validity of an argument depends only on the relation of the premises to the conclusion. In other words, the truth or falsity of an argument‘s conclusion does not by itself determine the validity or invalidity of that argument and, also, the fact that an argument is valid does not guarantee the truth of its conclusion. The illustrative arguments can be represented thus: I. Some valid arguments contain only true propositions – true premises and a true conclusion: All terrestrial beings live on earth. All humans are terrestrial beings. Therefore, all humans live on earth. II. Some valid arguments contain only false propositions – false premises and a false conclusion: All Cyclops have dark skin. All flying horses are Cyclops. Therefore, all flying horses have dark skin. This argument is valid because, if its premises were true, its conclusion would have to be true also, though, we know that in fact both the premises and the conclusion of this argument are false. 38 PHL 152 MODULE 2 III. Some invalid arguments contain only true propositions – all their premises are true, and their conclusions are true as well: If I bagged a bachelor‘s degree from the University of Ibadan, then I would be a graduate. I do not have a degree from the University of Ibadan. Therefore, I am not a graduate. The true conclusion of this argument does not follow from its true premises. The fact that I do not have a degree from the University of Ibadan does not presuppose that I am not a graduate. IV. Some invalid arguments contain only true premises and have a false conclusion. This is illustrated by an argument exactly like the previous example (III) in form, changed only enough to make the conclusion false. If Ade Babangida bagged a bachelor‘s degree from the University of Ibadan, then he would be a graduate. He does not have a degree from the University of Ibadan. Therefore, he is not a graduate. The premises of this argument are true, but its conclusion is false. This above example underscores our point that it is impossible for the premises of a valid argument to be true and its conclusion to be false. V. Some valid arguments have false premises and a true conclusion: All spiders belong to the cat family. All tigers are spiders. Therefore, tigers belong to the cat family. The conclusion of this argument is true and may be validly inferred from these two premises, both of which are wildly false. VI. Some invalid arguments also have false premises and a true conclusion: All arachnids have wings. All scorpions have wings. Therefore, all scorpions are arachnids. From examples V and VI taken together, it can be inferred that the validity or invalidity an argument does not depend on whether it has false premises and a true conclusion. VII. Some invalid arguments, of course, contain all false propositions – false premises and a false conclusion: All arachnids have wings. 39 PHL 152 INTRODUCTION TO LOGIC II All scorpions have wings. Therefore, all arachnids are scorpions. An argument is said to be sound if that argument is valid and has all its premises and conclusion as true. On the contrary, an argument is unsound if though valid, the premises fail to establish the truth of its conclusion. Thus, ―the conclusion of a sound argument obviously must be true – and only a sound argument can establish the truth of its conclusion. If a deductive argument is not sound – that is, if the argument is not valid or if not all its premises are true – it fails to establish the truth of its conclusion even if in fact the conclusion is true‖ (Copi & Cohen 2006: 15). Let‘s illustrate the difference between sound and unsound arguments with examples: (i) All elephants are herbivores All herbivores live on land Therefore, all elephants live on land. (ii) All university graduates are lawyers All lawyers are soothsayers Therefore, all university graduates are soothsayers. The first example is a sound argument, while the second is unsound because all the statements in the argument are false, though the argument is valid. Sample Exercises: (see Copi & Cohen 2006: 16) Construct a series of deductive arguments, on any subject of your choosing, each with only two premises, having the following characteristics: (i) A valid argument with one true premise, one false premise, and a false conclusion: Solution: Premise: Of all the rivers in the world, the Ganges in the largest. [False] Premise: Varanasi is on the banks of the Ganges River. [True] Conclusion: Therefore Varanasi is on the banks of the largest river in the world [False] (ii) A valid argument with two false premises and a true conclusion: Solution: Premise: In all countries of the world, the largest city in the capital. [False] Premise: Canberra is the largest city in Australia. [False] Conclusion: Therefore Canberra is the capital of Australia. [True] 40  PHL 152 MODULE 2 Self-Assessment Exercise 2 1. In a deductive argument, the premises conclusively or logically imply the conclusion; in an inductive argument, the premises only provide some ____________________ grounds for the acceptance of the conclusion. 2. The following are examples of what type of argument. a. All humans are mortal Aristotle is human Therefore, Aristotle is mortal. b. All humans are animals All animals are mortal Therefore, all humans are mortal. c. All Nigerians are Africans All Africans are coloured Therefore, all Nigerians are coloured. 3. What does it mean to say that a deductive argument is valid? Conclusion There are mainly two forms of arguments and these are deductive and inductive. Deductive argument has its premises supporting the conclusion while an inductive argument is one that the conclusion is made probable. A deductive argument can be valid, sound and unsound. All inductive arguments are both invalid and unsound. 2.4 Summary In this unit, we pointed out that there are distinguishing features between deductive and inductive arguments. We explained that if we are confronted with an argument whose truth of its premises guarantees the truth of its conclusion, then that argument is said to involve in a deductive inference. In other words, the conclusion of a deductive argument is claimed to follow from the premises with necessity, and a valid deductive argument is one in which conclusion is necessarily true if the premises are true. An inductive argument, on the other hand, is an argument whose conclusion has some degree of probability but for which the claim of necessity is not made. We went on to discuss the relations between the validity (or invalidity) of deductive arguments and the truth (or falsity) of their constituents propositions. 41 PHL 152 INTRODUCTION TO LOGIC II 2.5 References/Further Reading Ade-Ali, Samuel and Fadahunsi, Ayo, Introduction to Philosophy and Logic (Ibadan: Hope Publication, 1999). Lawhead, William F. The Voyage of Discovery: A Historical Introduction to Philosophy, (London: Wadsworth Group, 2002). Offor, Francis. Essentials of Logic (Ibadan: Book Wright Nigeria Publishers, 2010). Oke, Moses and Amodu, Akeem. Argument and Evidence: An Introduction to Critical Thinking (Ibadan: Hope Publications, 2006). Bello, A.G.A. Introduction to Logic (Ibadan: University Press Ltd., 2007) Copi, I.M., Cohen C. Introduction to Logic (London: Prentice-Hall, 1998) Dauer, F.W. Critical Thinking: An Introduction to Reasoning (Oxford: Oxford University Press,1989). Kalish, D., Montague, R., Mar G. Logic: Techniques of Formal Reasoning (New York: Harcourt Brace Jonanich, 1980). 42 PHL 152 MODULE 2 2.6 Possible Answer to Self-Assessment Exercise 2 1. Probable 2. Deductive argument 3. Is to say that it is not possible for its conclusion to be false if its premises are true. 43 PHL 152 INTRODUCTION TO LOGIC II UNT 3 INFORMAL FALLACIES I (FALLACIES OF RELEVANCE) Unit Structure 3.1 Introduction 3.2 Learning Outcomes 3.3 Fallacy 3.4 Informal Fallacy – The Fallacies of Relevance 3.4.1 Appeal to Force (argumentum ad baculum) 3.4.2 The Appeal to Pity (argumentum ad misericordiam) 3.4.3 The Appeal to Emotion (argumentum ad populum) 3.4.4 The Appeal to Inappropriate Authority (argumentum ad veracundiam) 3.4.5 Argument against the Man or Person (argumentum ad hominem) 3.4.6 Appeal to Ignorance (argumentum ad ignorantiam) 3.4.7 Irrelevant Conclusion (ignoratio elenchi) 3.4.8 Black-or-White Fallacy 3.5 Summary 3.6 References/Further Reading 3.7 Possible Answer to Self-Assessment Exercise 3.1 Introduction In our previous units, we have been able to show that, for us to have a good argument, the premises must support the conclusion. If otherwise, the argument is considered fallacious. Thus in this unit, we shall examine Informal Fallacy. We shall focus on a particular kinds of informal fallacies, The fallacies of relevance that are often unnoticed committed by some individuals. 3.2 Learning Outcomes By the end of this unit you should be able to:  define the term ―fallacy‖  distinguish between ―formal and ―informal fallacies.  state at least one defining characteristic of fallacies of relevance. 44 PHL 152 MODULE 2 3.3 Fallacy What is fallacy? When the premises of an argument fail to support its conclusion, the argument is said to be bad or, more technically, fallacious. When an argument exhibits a certain kind of mistake in reasoning, that argument is said to be fallacious, implying that a fallacy is any error we commit in reasoning. It should be added, however, that the term ―designates not only any errors in reasoning, but typical errors – mistakes in reasoning whose common pattern can be detected‖ (Copi & Cohen 2006:357). A fallacy is, therefore, ―a type of argument that may seem to be correct but that proves, on examination, not to be so‖ (Ibid). From the foregoing, it is clear that ―a fallacy has two features: first, it is an argument; second, its premises provide no support to the conclusion though they appear to do so, because the argument is psychologically persuasive‖ (Bello 2007:41). There are the ‗Formal‘ and ‗Informal‘ fallacies. Formal fallacies are the types of mistakes we make in our attempt to construct syllogisms (deductive reasoning/a logical argument with two premises and a conclusion) or in using logical symbols. Informal fallacies, on the other hand, are the types of errors in reasoning that occur as a result of carelessness or inattention to the content of the propositions constituting an argument. At this level, we shall focus on Informal Fallacies which can be classified into three broad categories, namely, fallacies of relevance, fallacies of ambiguity, and fallacies of presumption. In this lecture, we shall engage ourselves with Fallacies of Relevance. 3.3.1 Informal Fallacies (The fallacies of relevance) This is concern those arguments whose premises appear to be relevant to the conclusion drawn but, on close examination, are simply not relevant. These fallacies will now be examined. 3.3.2 The Appeal to Force (argumentum ad baculum) This fallacy is committed when one resorts to the use of threat to cause the acceptance of a conclusion, especially when evidence or rational methods fail. In other words, this fallacy is committed when an argument relies on the threat of force, though the threat may be veiled and may not necessarily be physical. For instance, I‘ll be committing this fallacy if I threaten to fail students who disagree with my political ideology. This means that the fallacy can be committed by someone in a position of power if he uses threat to coerce his opponents to accept his proffered proposition. The following are examples of arguments that commit this fallacy: 45 PHL 152 INTRODUCTION TO LOGIC II (i) All fresh students in the Department of Philosophy should attend my wedding if they want me to be lenient in assessing their exam scripts. (ii) If you do not agree with my political opinions, you will not graduate from this university. 3.3.3 The Appeal to Pity (argumentum ad misericordiam) Misericordiam means ―a pitying heart‖. Thus, this fallacy occurs when the premises of an argument plainly relies on mercy, generosity, altruism, and so on. For instance, a lawyer might use the special circumstances of his client (an offender) to justify leniency in punishment. In short, when the lawyer emphasizes the unfortunate consequences that will befall his client instead of looking at the overwhelming proof of his guilt, he has committed this fallacy. The following passages commit this fallacy: (i) I am a single parent, solely responsible for the financial support of my children. If you give me this traffic ticket, I will lose my license and be unable to drive to work. If I cannot work, my children and I will become homeless and may starve to death. Therefore, you should not give me this traffic ticket (Offor 2012: 42). (ii) I implore the jury to temper justice by mercy. Though my client, barely eighteen, is accused of killing his mother and father with an axe, I plead for leniency on the grounds that he is an orphan. 3.3.4 The Appeal to popular feeling/Mob appeal (argumentum ad populum) This fallacy is committed when, instead of using evidence and rational argument, you appeal to the emotion of the people to win their assent to a conclusion. The appeal to emotion, therefore, relies on expressive language and other devices to arouse strong feelings that may lead an audience to accept its conclusion. This fallacy is a device often used by politicians, propagandists, is common in commercial advertising. The following example explains this fallacy: (i) The wisest men and women in Yoruba history have all been interested in Ifa. Obas, queens and regents of all epochs in Yoruba land have believed in it and have guided the affairs of their people by it. Therefore those who say that Ifa is not a science are mistaken (Bello 2007: 53). (ii) In the last presidential campaign, a mammoth crowd welcomed 46 PHL 152 MODULE 2 Goodluck Jonathan in each of the northern zones. In the last election, he led the other presidential candidates with very wide margins and became president. Therefore, those who accuse Jonathan of financial misappropriation are not sincere. 3.3.5 The Appeal to Inappropriate Authority (argumentum ad verecundiam) This fallacy arises when we appeal to the opinions of someone who in fact does not have any legitimate claim to authority in the matter at hand. In other words, it ―involves the mistaken supposition that there is some connection between the truth of a proposition and some feature of the person who asserts or denies it‖ (Offor 2012: 42). For instance, it would be fallacious to appeal to the opinions of a movie star on whether taking a brand of beer is good for the body or not. Someone with expertise in food nutrition would be the appropriate authority. Thus, ―when the truth of some proposition is asserted on the basis of the authority of one who has no special competence in that sphere, the appeal to inappropriate authority is the fallacy committed‖ (Copi et al 2006: 374). Consider these examples: (i) Pato Ogundeji, a Professor of Linguistics and African Languages at the University of Ibadan, believes that the stars revolve round the earth in a perfect circle. Therefore, the stars revolve round the earth in a perfect circle. (ii) But can you doubt that air has weight when you have the clear testimony of Aristotle affirming that all the elements have weight including air, and excepting only fire? 3.3.6 Argument against the Man or Person (argumentum ad hominem) This is a fallacy in which the argument relies on an attack against the person taking a position. In other words, when the thrust of an argument is directed at someone who is defending a conclusion in dispute (and not the conclusion itself), the fallacy committed is ad hominem. There are two major forms of the ad hominem argument, namely, the ‗abusive‘ and the ‗circumstantial‘. The ‗abusive‘ variety of ad hominem is committed when one attacks the person who made an assertion, instead of giving reasons why the assertion should not be accepted. The ‗circumstantial‘ occurs when one argues against the circumstance of the opponent, instead of assessing the dispute in question. Consider the following examples: 47 PHL 152 INTRODUCTION TO LOGIC II Abusive (i) Mr. Brown‘s arguments for pre-marital sex should be dropped because he is a womanizer. (ii) Darwin‘s thesis of natural selection should be discarded as a work of fictionbecause he is a racist. Circumstantial (i) Rev. Father John should accept my position that abortion should be abolished because this is compatible with his faith as a Catholic. (ii) Former President Bush wouldn‘t approve of President Obama‘s economic policies because he is a Republican. 3.3.7 Appeal to Ignorance (argumentum ad ignorantiam) This fallacy is committed when one posits that a proposition is true simply because it has not been proved false or that it is false because it has not been proved true. Bello (2007: 52) adds that ―this mode of argument is commonly used to argue against the existence of witches, spirits, and other forms of extraordinary‘ phenomena‖. The following passages commit this fallacy: (i) No one has conclusively proven that there is no intelligent life on the moons of Jupiter. Therefore, there is intelligent life on the moons of Jupiter (Offor 2012: 43). (ii) The alarmists have not succeeded in proving that the toxic and radioactive materials dumped at Koko (Delta state) are dangerously harmful to human life. The materials are therefore perfectly safe (Bello 2007: 52). 3.3.8 Irrelevant Conclusion (ignoratio elenchi) Ignoratio elenchi translates to ―mistaken proof‖ and is a type of fallacy in which the premises provide justification or grounds for a different conclusion than the one that is proposed. It tries to establish the truth of a proposition with premises which actually provide support for an entirely different conclusion. The following are examples of this fallacy: (i) The Golden rule is basic to every system of ethics ever devised. Everyone accepts it in some form or other. Therefore, people‘s lives are guided by legislations (Offor 2012: 43) 48 PHL 152 MODULE 2 (ii) Capitalism is desirable. For at one time all utilities were state- owned; now more and more of them are being commercialised or privatised. The Structural Adjustment Programme (SAP), moreover, is based on capitalist principles. We are well on our way to full-blown capitalism and its complete triumph is inevitable (Bello 2007: 51). 3.3.9 Black-or-White Fallacy Also referred to as Fallacy of False Alternatives, this fallacy is committed when it is falsely assumed in an argument that only two alternatives or positions are possible with regard to a certain issue or when the possibility of a third alternative to the two already allowed is ignored (Bello, 2000). For example: (i) He who is not a PDP member is against Jonathan‘s regime Oshiomole is not a PDP member He is therefore against Jonathan‘s regime. (ii) He who does not preach the Word of God is an anti-Christ Bisala does not preach the Word of God. Therefore, he is an anti-Christ. Exercises: (see Copi & Cohen 2006: 367 – 370) Identify the fallacies of relevance in the following passages: (i) ICICI, a premier financial institution in the country is offering best financial product with value added services. It is not just finance but it is love and affection, which is being transacted. Most personalized service at your doorstep offered by the ICICI for housing finance seekers. Like a family member and a good friend ICICI fulfils your needs to have your sweet home. Solution: Appeal to Emotion is not (argumentum ad populum). The fallacy is quite common in advertisements. The uses of words like ―love‖, ―affection‖ and ―family‖ are used as such words are not usually associated with banks and it is an appeal to the emotions of people to try to tell them that ICICI is a friendly bank. (ii) When we had got to this point in the argument and everyone saw that the definition of justice had been completely upset, Thrasymachus, instead of replying me, said: ―Tell me, Socrates, have you got a nurse?‖ ― Why do you ask such a question,‖ I said, ―when you ought rather to be answering?‖ 49  PHL 152 INTRODUCTION TO LOGIC II ― Because she leaves you to snivel, and never wipes your nose; she has not even taught you to know the shepherd from the sheep.‖ Solution: Argument Against the Person (argumentum ad hominem), ‗Abusive‘. Self-Assessment Exercise 3 1. __________________________ is an error we commit in reasoning. 2. A fallacy is committed when one resorts to the use of threat to cause the acceptance of a conclusion. 3. Argument against a person can be alternatively called _______________________ Conclusion All forms of the fallacies of relevance are incorrect way of reasoning because they violate the logical principles of thought. 3.4 Summary In this unit, we defined the term ―fallacy‖ as any error we commit in reasoning. We pointed out that Informal Fallacy can be classified into three broad categories, namely, fallacies of relevance, fallacies of ambiguity, and fallacies of presumption. This unit was devoted to fallacies of relevance, whose premises appear to be relevant to the conclusion drawn but, on close examination, are simply not relevant. Under fallacies of relevance, we discussed The Appeal to Force (argumentum ad baculum) which is committed when one resorts to the use of threat to cause the acceptance of a conclusion, especially when evidence or rational methods fail. The Appeal to Pity (argumentum ad misericordiam) occurs when the premises of an argument plainly relies on mercy, generosity, altruism, and so on. You also read that The Appeal to Emotion (argumentum ad populum) relies on expressive language and other devices to arouse strong feelings that may lead an audience to accept its conclusion The unit also made you to understand that The Appeal to Inappropriate Authority (argumentum ad verecundiam) which arises when we appeal to the opinions of someone who in fact does not have any legitimate claim to authority in the matter at hand. Argument Against the Man or Person (argumentum ad hominem), a fallacy in which the argument relies on an attack against the person taking a position and there are two types, abusive or 50 PHL 152 MODULE 2 circumstantial. Appeal to Ignorance (argumentum ad ignorantiam) which is committed when one posits that a proposition is true simply because it has not been proved false or that it is false because it has not been proved true; Irrelevant Conclusion (ignoratio elenchi), a type of fallacy in which the premises provide justification or grounds for a different conclusion than the one that is proposed; Black-or-White Fallacy which is committed when it is falsely assumed in an argument that only two alternatives or positions are possible in regards with a certain issue or when the possibility of a third alternative to the two already allowed is ignored. 3.5 References/Further Reading/Web Resources