Critical Thinking: A Student's Introduction (4th Edition) PDF

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fourth EDItION fourth EDItION Critical Thinking This clear, learner-friendly text helps today’s students bridge the gap between A student ' s Introduction Critical Thinking everyday culture and critical thinking. It covers all the basics of critical A student's Introduction thinking, using real-world examples and a proven step-by-step approach. Its comprehensiveness allows instructors to tailor the material to their individual teaching styles, resulting in an exceptionally versatile text. Highlights of the Fourth Edition: Additional readings and essays in a new Appendix as well as in Chapters 7 and 8 nearly double the number of readings available for critical analysis and classroom discussion. An online chapter, available on the instructor portion of the book’s Web site, addresses critical reading, a vital skill for success in college and beyond. Chapter 12 features an expanded and reorganized discussion of evaluating MD DALIM #1062017 12/13/09 CYAN MAG YELO BLK Internet sources. New and updated exercises and examples throughout the text allow students to practice and apply what they learn. Nardone I Wallace Bassham I Irwin Visit www.mhhe.com/bassham4e for a wealth of additional student and instructor resources. Ba ssha m I Irwin I Nardone I Wall ace  CRITICAL THINKING A STUDENT’S INTRODUCTION FOURTH EDITION Gregory Bassham William Irwin Henry Nardone James M. Wallace King’s College TM bas07437_fm_i-xvi.indd i 11/24/09 9:53:56 AM  TM Published by McGraw-Hill, an imprint of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2011, 2008, 2005, 2002. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other elec- tronic storage or transmission, or broadcast for distance learning. This book is printed on acid-free paper. 1 2 3 4 5 6 7 8 9 0 DOC/DOC 0 ISBN: 978-0-07-340743-2 MHID: 0-07-340743-7 Vice President, Editorial: Michael Ryan Director, Editorial: Beth Mejia Sponsoring Editor: Mark Georgiev Marketing Manager: Pam Cooper Managing Editor: Nicole Bridge Developmental Editor: Phil Butcher Project Manager: Lindsay Burt Manuscript Editor: Maura P. Brown Design Manager: Margarite Reynolds Cover Designer: Laurie Entringer Production Supervisor: Louis Swaim Composition: 11/12.5 Bembo by MPS Limited, A Macmillan Company Printing: 45# New Era Matte, R. R. Donnelley & Sons Cover Image: © Brand X/JupiterImages Credits: The credits section for this book begins on page C-1 and is considered an extension of the copyright page. Library of Congress Cataloging-in-Publication Data Critical thinking : a student’s introduction / Gregory Bassham... [et al.].—4th ed. p. cm. Includes bibliographical references and index. ISBN 978-0-07-340743-2 (alk. paper) 1. Critical thinking—Textbooks. I. Bassham, Gregory, 1959– B809.2.C745 2010 160—dc22 2009034761 The Internet addresses listed in the text were accurate at the time of publication. The inclusion of a Web site does not indicate an endorsement by the authors or McGraw-Hill, and McGraw-Hill does not guarantee the accuracy of the information presented at these sites. www.mhhe.com bas07437_fm_i-xvi.indd ii 11/24/09 9:53:56 AM  For Enrico, Eric, Nicole, Dylan, Catherine, Daniel, and Kate bas07437_fm_i-xvi.indd iii 11/24/09 9:53:57 AM bas07437_fm_i-xvi.indd iv 11/24/09 9:53:57 AM  CONTENTS A Word to Students xi Preface xiii CHAPTER 1 Introduction to Critical Thinking 1 What Is Critical Thinking? 1 Critical Thinking Standards 2 Clarity 2 Precision 2 Accuracy 3 Relevance 3 Consistency 4 Logical Correctness 5 Completeness 6 Fairness 6 The Benefits of Critical Thinking 7 Critical Thinking in the Classroom 7 Critical Thinking in the Workplace 9 Critical Thinking in Life 9 Barriers to Critical Thinking 10 Egocentrism 11 Sociocentrism 13 Unwarranted Assumptions and Stereotypes 16 Relativistic Thinking 19 Wishful Thinking 24 Characteristics of a Critical Thinker 25 v bas07437_fm_i-xvi.indd v 11/26/09 6:18:25 PM  vi Contents CHAPTER 2 Recognizing Arguments 29 What Is an Argument? 29 Identifying Premises and Conclusions 33 What Is Not an Argument? 40 Reports 40 Unsupported Assertions 41 Conditional Statements 41 Illustrations 43 Explanations 43 CHAPTER 3 Basic Logical Concepts 53 Deduction and Induction 53 How Can We Tell Whether an Argument Is Deductive or Inductive? 56 The Indicator Word Test 57 The Strict Necessity Test 58 The Common Pattern Test 58 The Principle of Charity Test 59 Exceptions to the Strict Necessity Test 61 Common Patterns of Deductive Reasoning 62 Hypothetical Syllogism 62 Categorical Syllogism 65 Argument by Elimination 66 Argument Based on Mathematics 66 Argument from Definition 67 Common Patterns of Inductive Reasoning 67 Inductive Generalization 68 Predictive Argument 68 Argument from Authority 69 Causal Argument 69 Statistical Argument 70 Argument from Analogy 70 Deductive Validity 73 Inductive Strength 77 CHAPTER 4 Language 86 Finding the Right Words: The Need for Precision 86 Vagueness 87 Overgenerality 88 Ambiguity 89 bas07437_fm_i-xvi.indd vi 11/24/09 9:53:57 AM  Contents vii The Importance of Precise Definitions 93 Types of Definitions 95 Strategies for Defining 97 Rules for Constructing Good Lexical Definitions 100 Emotive Language: Slanting the Truth 107 The Emotive Power of Words 108 Euphemisms and Political Correctness 114 CHAPTER 5 Logical Fallacies—I 119 The Concept of Relevance 119 Fallacies of Relevance 121 Personal Attack (Ad Hominem) 122 Attacking the Motive 123 Look Who’s Talking ( Tu Quoque) 124 Two Wrongs Make a Right 125 Scare Tactics 127 Appeal to Pity 128 Bandwagon Argument 128 Straw Man 129 Red Herring 130 Equivocation 131 Begging the Question 132 CHAPTER 6 Logical Fallacies—II 140 Fallacies of Insufficient Evidence 140 Inappropriate Appeal to Authority 140 Appeal to Ignorance 144 False Alternatives 145 Loaded Question 146 Questionable Cause 147 Hasty Generalization 149 Slippery Slope 150 Weak Analogy 151 Inconsistency 154 CHAPTER 7 Analyzing Arguments 164 Diagramming Short Arguments 164 Tips on Diagramming Arguments 169 Summarizing Longer Arguments 175 Paraphrasing 176 bas07437_fm_i-xvi.indd vii 11/28/09 11:42:14 AM  viii Contents Finding Missing Premises and Conclusions 180 Summarizing Extended Arguments 182 Common Mistakes to Avoid in Standardizing Arguments 187 CHAPTER 8 Evaluating Arguments and Truth Claims 195 When Is an Argument a Good One? 195 What “Good Argument” Does Not Mean 195 What “Good Argument” Does Mean 196 When Is It Reasonable to Accept a Premise? 198 Refuting Arguments 203 Appendix: Sample Critical Essay 219 CHAPTER 9 A Little Categorical Logic 225 Categorical Statements 225 Translating into Standard Categorical Form 230 Categorical Syllogisms 237 CHAPTER 10 A Little Propositional Logic 252 Conjunction 253 Conjunction and Validity 256 Negation 261 Deeper Analysis of Negation and Conjunction 265 Disjunction 271 Conditional Statements 276 CHAPTER 11 Inductive Reasoning 285 Introduction to Induction 285 Inductive Generalizations 286 Evaluating Inductive Generalizations 288 Opinion Polls and Inductive Generalizations 292 Statistical Arguments 296 Reference Class 300 Induction and Analogy 303 What Is an Analogy? 303 How Can We Argue by Analogy? 303 bas07437_fm_i-xvi.indd viii 12/2/09 2:26:59 PM  Contents ix Evaluating Arguments from Analogy 305 Arguing by Analogy 312 Induction and Causal Arguments 313 Correlation and Cause 317 A Few Words about Probability 320 A Closer Look at a Priori Probability 322 CHAPTER 12 Finding, Evaluating, and Using Sources 330 Finding Sources 333 Refining Your Search: Questions and Keywords 334 Directional Information 336 Informational Sources 338 Evaluating Sources 341 Content: Facts and Everything Else 342 The Author and the Publisher 347 The Audience 352 Evaluating Internet Sources 353 Taking Notes 361 Bibliographical Information 361 Content Notes: Quotes, Summaries, and Paraphrases 362 Using Sources 372 Acknowledging Sources 372 Incorporating Sources 376 CHAPTER 13 Writing Argumentative Essays 382 Writing a Successful Argument 384 Before You Write 385 Know Yourself 385 Know Your Audience 386 Choose and Narrow Your Topic 390 Write a Sentence That Expresses Your Claim 393 Gather Ideas: Brainstorm and Research 394 Organize Your Ideas 400 Organize by Methods of Development 403 Writing the First Draft 406 Provide an Interesting Opening 407 Include a Thesis Statement 408 Develop Your Body Paragraphs 409 Provide a Satisfying Conclusion 410 bas07437_fm_i-xvi.indd ix 11/24/09 9:53:57 AM  x Contents After the First Draft 412 Read What You Have Written and Revise 412 Consider What You Have Not Written and Revise 412 Show Your Work 413 Edit Your Work 413 Hand It In 413 Sample Argumentative Essay 414 CHAPTER 14 Thinking Critically about the Media 425 The Mass Media 425 The News Media 426 The Importance of Context 426 Getting Us to Pay Attention: What Really Drives the Media 430 Keeping Our Interest: The News as Entertainment 432 How the Media Entertain Us 433 Slanting the News 441 Media Literacy 445 Advertising 447 What Ads Do 448 Defenses of Advertising 450 Criticisms of Advertising 450 Common Advertising Ploys 452 CHAPTER 15 Science and Pseudoscience 461 The Basic Pattern of Scientific Reasoning 461 The Limitations of Science 468 How to Distinguish Science from Pseudoscience 470 A Case Study in Pseudoscientific Thinking: Astrology 482 Appendix: Essays for Critical Analysis A-1 Notes N-1 Answers to Selected Exercises ANS-1 Credits C-1 Index I-1 bas07437_fm_i-xvi.indd x 11/24/09 9:53:57 AM  A WORD TO STUDENTS L et’s be honest. Very few of your college textbooks will change your life. But this one truly can. This book will make you a better thinker. It will sharpen your mind, clarify your thoughts, and help you make smarter decisions. We’ll teach you—step by step—how to analyze issues, reason logically, and argue effectively. With effort on your part, this book will hone the think- ing and reasoning skills you need to succeed in college, in your career, and in life. Critical thinking is what college is all about. College is not about cram- ming students’ heads with facts. It’s about teaching students to think. And that’s precisely what this book is designed to do. It will help you develop the skills and dispositions you need to become an independent, self-directed thinker and learner. Collectively, the four authors of this textbook have been teaching criti- cal thinking for over 60 years. Teaching critical thinking is what we do. It’s our passion. We’ve seen how critical thinking can change lives. But you’ll only get out of this course what you put into it. Becoming a critical thinker is hard work. Sometimes working through this book will feel a little like boot camp. There’s a reason for this: No pain, no gain. Becoming a master thinker means toning up your mental muscles and acquiring habits of careful, disciplined thinking. This requires effort, and practice. That’s why the heart of this textbook is the exercises. There are lots of these, and all have been carefully selected and class-tested. You need to do the exercises. As many as you can. (Or at least all that your instructor assigns.) Do the exercises, then check the answers at the back of the book. Practice. Make mistakes. Get feedback. And watch yourself improve. That’s how you’ll work the mental flab off and develop lasting habits of clear, rigorous thinking. Critical thinking is an adventure. Becoming mentally fit is hard work. And thinking independently can be a little scary at times. But in the end you’ll be a smarter, stronger, more confident thinker. xi bas07437_fm_i-xvi.indd xi 11/24/09 9:53:57 AM bas07437_fm_i-xvi.indd xii 11/24/09 9:53:57 AM  PREFACE Nothing is more powerful than reason. —Saint Augustine T he first edition of Critical Thinking: A Student’s Introduction grew out of our conviction that a critical thinking text that works—that produces real, measurable improvement in students’ critical reasoning skills—must have two essential features: It must be a text that our increasingly gadget-oriented students actually read. It must provide abundant, class-tested exercises that give students the practice they need to develop as maturing critical thinkers. In revising Critical Thinking: A Student’s Introduction for this edition, we’ve tried to remain faithful to this original vision. Many passages have been rewritten to make the book clearer and (we hope) more engaging and accessible. In addition, dozens of new exercises have been added to give stu- dents even more opportunities to hone their critical reasoning skills. OVERVIEW OF THE TEXT Critical Thinking: A Student’s Introduction is designed to provide a versatile and comprehensive introduction to critical thinking. The book is divided into seven major parts: 1. The Fundamentals: Chapters 1–3 introduce students to the basics of critical thinking in clear, reader-friendly language. 2. Language: Chapter 4 discusses the uses and pitfalls of language, emphasizing the ways in which language is used to hinder clear, effective thinking. xiii bas07437_fm_i-xvi.indd xiii 11/24/09 9:53:57 AM  xiv Preface 3. Fallacies: Chapters 5 and 6 teach students how to recognize and avoid twenty of the most common logical fallacies. 4. Argument Analysis and Evaluation: Chapters 7 and 8 offer a clear, step-by-step introduction to the complex but essential skills of argument analysis and evaluation. 5. Traditional Topics in Informal Logic: Chapters 9–11 offer a clear, sim- plified introduction to three traditional topics in informal logic: categorical logic, propositional logic, and inductive reasoning. 6. Researching and Writing Argumentative Essays: Chapters 12 and 13 provide students with specific, detailed guidance in producing well-researched, properly documented, and well-written argumen- tative essays. 7. Practical Applications: Chapters 14 and 15 invite students to apply what they have learned by reflecting critically on two areas in which uncritical thinking is particularly common: the media (Chapter 14) and pseudoscience and the paranormal (Chapter 15). The text can be taught in a variety of ways. For instructors who stress argument analysis and evaluation, we suggest Chapters 1–8. For instructors who emphasize informal logic, we recommend Chapters 1–6 and 9–11. For instructors who focus on writing, we suggest Chapters 1–6 and 12 and 13. And for instructors who stress practical applications of critical thinking, we recommend Chapters 1–6 and 14 and 15. STRENGTHS AND DISTINCTIVE FEATURES OF THE TEXT There are a number of features that set this book apart from other critical thinking texts: A versatile, student-centered approach that covers all the basics of critical thinking—and more—in reader-friendly language An abundance of interesting (and often humorous or thought- provoking) classroom-tested exercises An emphasis on active, collaborative learning A strong focus on writing, with complete chapters on using and evaluating sources (Chapter 12) and writing argumentative essays (Chapter 13) An emphasis on real-world applications of critical thinking, with many examples taken from popular culture, and complete chapters on the media and pseudoscientific thinking bas07437_fm_i-xvi.indd xiv 11/24/09 9:53:58 AM  Preface xv An extensive treatment of critical thinking standards, hindrances, and dispositions A clear and detailed discussion of the distinction between deductive and inductive reasoning An abundance of thought-provoking marginal quotes, as well as “Critical Thinking Lapses”—outrageous errors in reasoning and thinking An Online Learning Center that includes detailed chapter summa- ries, tutorials, and quizzes on the Web at www.mhhe.com/bassham4e For the instructor, a password-protected, user-friendly Instructor’s Manual that includes complete answer keys, teaching tips, sample tests and quizzes, and PowerPoint lecture notes WHAT’S NEW TO THE FOURTH EDITION In preparing this edition, we have benefited tremendously from suggestions from users and reviewers of previous editions. The major changes in this edition are these: A new Appendix has been added, featuring seven new essays for critical analysis. A new chapter on critical reading is available to course adopters on the Instructor’s part of the book’s Web site. Chapter 12 features an expanded and reorganized discussion of evaluating Internet sources. A new sample critical essay has been added, and the sample argu- mentative essay has been substantially revised. New readings have been added to Chapters 7 and 8. Many new marginal quotes and boxed passages have been added. Several chapters have been streamlined. New and updated exercises and examples have been added throughout the book. Both the Instructor’s Manual and student online support resources have been updated and expanded. A module on the counterexample method of proving invalidity has been added to the Instructor’s Manual. bas07437_fm_i-xvi.indd xv 11/24/09 9:53:58 AM  xvi Preface ACKNOWLEDGMENTS For valuable feedback leading to this fourth edition we wish to thank Chris Blakey (College of the Canyons), David Campbell (Humboldt State Univer- sity), Arthur Hadley (Lincoln College of Technology), Brian Barnes (Uni- versity of Louisville), Cecilia Mun (College of Southern Nevada), Dorcas Chung (California State University–Sacramento), Janet Dumond (King’s College), and Robert Sessions (Kirkwood Community College). Our con- tinued thanks to reviewers of the previous editions: Dan Barwick, David Bowen, James Brooks, Barbara Carlson, B. Steve Csaki, Rory Conces, David Detmer, Andrew Dzida, Thomson Faller, Barbara Forrest, Mary Elizabeth Gleason, Claude Gratton, Perry Hardison, Jann James, Leemon McHenry, Tom MacMillan, Marty Most, Nikolas Pappas, Christopher H. Pearson, Ted Schick, and Corin Sutherland. It is a pleasure to pay tribute to the skilled and courteous people at McGraw-Hill who guided us through the production process, especially Phil Butcher, Lindsay Burt, Nicole Bridge, and David Blatty. Finally, thanks to our families for generously giving us the time to write. Without their love and support, this new edition could never have been completed. bas07437_fm_i-xvi.indd xvi 11/24/09 9:53:58 AM  CHAPTER 1 INTRODUCTION TO CRITICAL THINKING T his book is about the power of disciplined thinking. It’s about learning to think for yourself and being your own person. It’s about the personal empow- erment and enrichment that result from learning to use your mind to its fullest potential. In short, it’s about critical thinking. Critical thinking is what a college education is all about. In many high schools, the emphasis tends to be on “lower-order thinking.” Students are simply The function of expected to passively absorb information and then repeat it back on tests. In col- education is to lege, by contrast, the emphasis is on fostering “higher-order thinking”: the active, teach one to think intelligent evaluation of ideas and information. This doesn’t mean that factual intensively and to information and rote learning are ignored in college. But it is not the main goal think critically. of a college education to teach students what to think. The main goal is to teach —Martin Luther students how to think—that is, how to become independent, self-directed think- King Jr. ers and learners. WHAT IS CRITICAL THINKING? The purpose which runs Often when we use the word critical we mean “negative and fault-finding.” through all other This is the sense we have in mind, for example, when we complain about a educational parent or a friend who we think is unfairly critical of what we do or say. But critical also means “involving or exercising skilled judgment or observation.” purposes—the In this sense critical thinking means thinking clearly and intelligently. More common thread precisely, critical thinking is the general term given to a wide range of cogni- of education—is tive skills and intellectual dispositions needed to effectively identify, analyze, the development and evaluate arguments and truth claims; to discover and overcome personal of the ability to preconceptions and biases; to formulate and present convincing reasons in sup- think. port of conclusions; and to make reasonable, intelligent decisions about what —Educational Policies to believe and what to do. Commission Put somewhat differently, critical thinking is disciplined thinking governed by clear intellectual standards. Among the most important of these intellectual 1 bas07437_ch01_001-028.indd 1 11/24/09 8:00:16 AM  2 CHAPTER 1 Introduction to Critical Thinking standards are clarity, precision, accuracy, relevance, consistency, logical cor- rectness, completeness, and fairness.1 Let’s begin our introduction to critical thinking by looking briefly at each of these important critical thinking standards. CRITICAL THINKING STANDARDS Clarity Before we can effectively evaluate a person’s argument or claim, we need to understand clearly what he or she is saying. Unfortunately, that can be difficult Everything that because people often fail to express themselves clearly. Sometimes this lack of can be said can be clarity is due to laziness, carelessness, or a lack of skill. At other times it results said clearly. from a misguided effort to appear clever, learned, or profound. Consider the —Ludwig Wittgenstein following passage from philosopher Martin Heidegger’s influential but notori- ously obscure book Being and Time: Temporality makes possible the unity of existence, facticity, and falling, and in this way constitutes primordially the totality of the structure of care. The items of care have not been pieced together cumulatively any more than temporality itself has been put together “in the course of time” [“mit der Zeit”] out of the future, the having been, and the Present. Temporality “is” not an entity at all. It is not, but it temporalizes itself.... Temporality temporalizes, and indeed it tempo- ralizes possible ways of itself. These make possible the multiplicity of Dasein’s modes of Being, and especially the basic possibility of authentic or inauthentic existence.2 That may be profound, or it may be nonsense, or it may be both. Whatever exactly it is, it is quite needlessly obscure. As William Strunk Jr. and E. B.White remark in their classic The Elements of Style, “[M]uddiness is not merely a disturber of prose, it is also a destroyer Confusion has its of life, of hope: death on the highway caused by a badly worded road sign, costs. heartbreak among lovers caused by a misplaced phrase in a well-intentioned —Crosby, Stills, and Nash letter....”3 Only by paying careful attention to language can we avoid such needless miscommunications and disappointments. Critical thinkers not only strive for clarity of language but also seek max- imum clarity of thought. As self-help books constantly remind us, to achieve our personal goals in life we need a clear conception of our goals and priori- ties, a realistic grasp of our abilities, and a clear understanding of the problems and opportunities we face. Such self-understanding can be achieved only if we Clarity is not value and pursue clarity of thought. a mere embel- lishment of the Precision intellect; it is the very heart of intel- Detective stories contain some of the most interesting examples of critical lectual virtue. thinking in fiction. The most famous fictional sleuth is, of course, Sherlock —Charles Larmore Holmes, the immortal creation of British writer Sir Arthur Conan Doyle. In Doyle’s stories Holmes is often able to solve complex mysteries when the bas07437_ch01_001-028.indd 2 11/24/09 8:00:17 AM  Critical Thinking Standards 3 bungling detectives from Scotland Yard haven’t so much as a clue. What is the secret of his success? An extraordinary commitment to precision. First, by care- ful and highly trained observation, Holmes is able to discover clues that others have overlooked. Then, by a process of precise logical inference, he is able to reason from those clues to discover the solution to the mystery. Everyone recognizes the importance of precision in specialized fields such as medicine, mathematics, architecture, and engineering. Critical thinkers also understand the importance of precise thinking in daily life. They under- stand that to cut through the confusions and uncertainties that surround many Really valuable everyday problems and issues, it is often necessary to insist on precise answers ideas can only be to precise questions: What exactly is the problem we’re facing? What exactly had at the price of are the alternatives? What exactly are the advantages and disadvantages of each close attention. alternative? Only when we habitually seek such precision are we truly critical —Charles S. Peirce thinkers. Accuracy There is a well-known saying about computers: “Garbage in, garbage out.” Simply put, this means that if you put bad information into a computer, bad information is exactly what you will get out of it. Much the same is true of human thinking. No matter how brilliant you may be, you’re almost guaran- teed to make bad decisions if your decisions are based on false information. A good example of this is provided by America’s long and costly involve- ment in Vietnam. The policymakers who embroiled us in that conflict were not stupid. On the contrary, they were, in journalist David Halberstam’s oft- quoted phrase, “the best and the brightest” of their generation. Of course, the reasons for their repeated failures of judgment are complex and controversial; No one can navi- but much of the blame, historians agree, must be placed on false and inad- gate well through equate information: ignorance of Vietnamese history and culture, an exagger- life without an ated estimate of the strategic importance of Vietnam and Southeast Asia, false accurate map by assumptions about the degree of popular support in South Vietnam, unduly which to steer. optimistic assessments of the “progress” of the war, and so on. Had American Knowledge is the policymakers taken greater pains to learn the truth about such matters, it is possession of such likely they would not have made the poor decisions they did. a map, and truth Critical thinkers don’t merely value the truth; they have a passion for is what the map accurate, timely information. As consumers, citizens, workers, and parents, gives us, linking us they strive to make decisions that are as informed as possible. In the spirit of to reality. Socrates’ famous statement that the unexamined life is not worth living, they —Tom Morris never stop learning, growing, and inquiring. Relevance Anyone who has ever sat through a boring school assembly or watched a mud-slinging political debate can appreciate the importance of staying focused on relevant ideas and information. A favorite debaters’ trick is to try to distract an audience’s attention by raising an irrelevant issue. Even bas07437_ch01_001-028.indd 3 11/24/09 8:00:17 AM  4 CHAPTER 1 Introduction to Critical Thinking Abraham Lincoln wasn’t above such tricks, as the following story told by his law partner illustrates: In a case where Judge [Stephen T.] Logan—always earnest and grave—opposed him, Lincoln created no little merriment by his reference to Logan’s style of dress. He carried the surprise in store for the latter, till he reached his turn before the jury. Addressing them, he said: “Gentlemen, you must be careful and not permit yourselves to be overcome by the eloquence of counsel for the defense. Judge Logan, I know, is an effective lawyer. I have met him too often to doubt that; but shrewd and careful though he be, still he is sometimes wrong. Since this trial has begun I have discovered that, with all his caution and fastidiousness, he hasn’t knowledge enough to put his shirt on right.” Logan turned red as crim- No tedious and son, but sure enough, Lincoln was correct, for the former had donned a new irrelevant dis- shirt, and by mistake had drawn it over his head with the pleated bosom behind. The general laugh which followed destroyed the effect of Logan’s eloquence cussion can be over the jury—the very point at which Lincoln aimed.4 allowed; what is said should be Lincoln’s ploy was entertaining and succeeded in distracting the attention of pertinent. the jury. Had the jurors been thinking critically, however, they would have real- —Plato ized that carelessness about one’s attire has no logical relevance to the strength of one’s arguments. Consistency It is easy to see why consistency is essential to critical thinking. Logic tells us that if a person holds inconsistent beliefs, at least one of those beliefs must be false. Critical thinkers prize truth and so are constantly on the lookout for inconsisten- cies, both in their own thinking and in the arguments and assertions of others. There are two kinds of inconsistency that we should avoid. One is logical The guiding prin- inconsistency, which involves saying or believing inconsistent things (i.e., things ciple of rational that cannot both or all be true) about a particular matter. The other is practical behavior is consis- inconsistency, which involves saying one thing and doing another. tency. Sometimes people are fully aware that their words conflict with their —Deborah J. deeds. The politician who cynically breaks her campaign promises once she Bennett takes office, the TV evangelist caught in an extramarital affair, the drug coun- selor arrested for peddling drugs—such people are hypocrites pure and simple. From a critical thinking point of view, such examples are not especially inter- esting. As a rule, they involve failures of character to a greater degree than they do failures of critical reasoning. More interesting from a critical thinking standpoint are cases in which people are not fully aware that their words conflict with their deeds. Such cases highlight an important lesson of critical thinking: that human beings often display a remarkable capacity for self-deception. Author Harold Kushner cites an all-too-typical example: Ask the average person which is more important to him, making money or being devoted to his family, and virtually everyone will answer family without hesitation. But watch how the average person actually lives out his life. See bas07437_ch01_001-028.indd 4 11/24/09 8:00:17 AM  Critical Thinking Standards 5 Speaking of Inconsistency... Philosophy professor Kenneth R. Merrill trap and has kept his shoulder to the offers the following tongue-in-cheek ad- wheel. vice for writers. What kind of inconsistency 6. Keep your language simple. Eschew ses- does Merrill commit? quipedalian locutions and fustian rhet- oric. Stay clear of the crepuscular—nay, 1. Watch your spelling. Writters who mis- tenebrific and fuliginous—regions of pele a lott of words are propperly re- orotund sonorities. guarded as iliterate. 7. Avoid vogue words. Hopefully, the writer 2. Don’t forget the apostrophe where its will remember that her words basically needed, but don’t stick it in where impact the reader at the dynamic inter- theres no need for it. A writers reputa- face of creative thought and action. To tion hangs on such trif le’s. be viable, the writer’s parameters must 3. Don’t exaggerate. Overstatement always enable her to engage the knowledgeable causes infinite harm. reader in a meaningful dialogue— 4. Beware of the dangling participle. For- especially at this point in time, when getting this admonition, infelicitous people tend to prioritize their priorities phrases creep into our writing. optimally. 5. Clichés should be avoided like the 8. Avoid profane or abusive language. It is plague. However, hackneyed language a damned outrage how many knuckle- is not likely to be a problem for the dragging slobs vilify people they dis- writer who, since he was knee-high to a agree with.5 grasshopper, has built a better mouse- where he really invests his time and energy, and he will give away the fact that he really does not live by what he says he believes. He has let himself be persuaded There is a dif- that if he leaves for work earlier in the morning and comes home more tired ference between at night, he is proving how devoted he is to his family by expending himself to knowing the path provide them with all the things they have seen advertised.6 and walking the Critical thinking helps us become aware of such unconscious practical incon- path. sistencies, allowing us to deal with them on a conscious and rational basis. —Morpheus, in The Matrix It is also common, of course, for people to unknowingly hold inconsis- tent beliefs about a particular subject. In fact, as Socrates pointed out long ago, such unconscious logical inconsistency is far more common than most people suspect. As we shall see, for example, many today claim that “morality is rela- tive,” while holding a variety of views that imply that it is not relative. Critical thinking helps us recognize such logical inconsistencies or, still better, avoid Intelligence means them altogether. a person who can Logical Correctness see implications and arrive at con- To think logically is to reason correctly—that is, to draw well-founded conclu- clusions. sions from the beliefs we hold. To think critically we need accurate and well- —Talmud supported beliefs. But, just as important, we need to be able to reason from those bas07437_ch01_001-028.indd 5 11/24/09 8:00:17 AM  6 CHAPTER 1 Introduction to Critical Thinking Man is the Rea- Critical Thinking Lapse soning Animal. The human race are masters of the ridiculous. There was actually a story Such is the claim. in our newspaper of a man who was bitten on the tongue while kissing a I think it is open rattlesnake. He decided to try a nonscientific remedy he heard about to to dispute. Indeed, counteract a snakebite. So he wired his mouth to a pickup truck battery my experiments and tried to jump-start his tongue. It knocked him out and he ended up in the hospital, where he lost part of his tongue and one lip.7 have proven to me that he is the Un- reasoning Animal. beliefs to conclusions that logically follow from them. Unfortunately, illogical Note his history. thinking is all too common in human affairs. Bertrand Russell, in his classic... His record is essay “An Outline of Intellectual Rubbish,” provides an amusing example: the fantastic re- cord of a maniac. I am sometimes shocked by the blasphemies of those who think themselves —Mark Twain pious—for instance, the nuns who never take a bath without wearing a bathrobe all the time. When asked why, since no man can see them, they reply: “Oh, but you forget the good God.” Apparently they conceive of the deity as a Peeping Tom, whose omnipotence enables Him to see through bathroom walls, but who is foiled by bathrobes. This view strikes me as curious.8 As Russell observes, from the proposition 1. God sees everything. the pious nuns correctly drew the conclusion 2. God sees through bathroom walls. However, they failed to draw the equally obvious conclusion that 3. God sees through bathrobes. Such illogic is, indeed, curious—but not, alas, uncommon. Completeness It is only when In most contexts, we rightly prefer deep and complete thinking to shallow and there is complete- superficial thinking. Thus, we justly condemn slipshod criminal investigations, ness and exhaus- hasty jury deliberations, superficial news stories, sketchy driving directions, tiveness that there and snap medical diagnoses. Of course, there are times when it is impossible or is scholarship. inappropriate to discuss an issue in depth; no one would expect, for example, a —Hsün Tzu thorough and wide-ranging discussion of the ethics of human genetic research in a short newspaper editorial. Generally speaking, however, thinking is better when it is deep rather than shallow, thorough rather than superficial. It is not much Fairness good thinking of a thing unless you Finally, critical thinking demands that our thinking be fair—that is, open- think it out. minded, impartial, and free of distorting biases and preconceptions.That can be —H. G. Wells very difficult to achieve. Even the most superficial acquaintance with history and the social sciences tells us that people are often strongly disposed to resist bas07437_ch01_001-028.indd 6 11/24/09 8:00:17 AM  The Benefits of Critical Thinking 7 unfamiliar ideas, to prejudge issues, to stereotype outsiders, and to identify truth with their own self-interest or the interests of their nation or group. It Closed-mindedness is probably unrealistic to suppose that our thinking could ever be completely means premature free of biases and preconceptions; to some extent we all perceive reality in intellectual old ways that are powerfully shaped by our individual life experiences and cultural age. backgrounds. But as difficult as it may be to achieve, basic fair-mindedness is —John Dewey clearly an essential attribute of a critical thinker. E XERCISE 1.1 I. Break into groups of four or five. Choose one member of your group to take notes and be the group reporter. Discuss your education up to this point. To what extent has your education prepared you to think clearly, precisely, ac- curately, logically, and so forth? Have you ever known a person (e.g., a teacher or a parent) who strongly modeled the critical thinking standards discussed in this section? If so, how did he or she do that? II. Have you ever been guilty of either practical inconsistency (saying one thing and doing another) or logical inconsistency (believing inconsistent things about a particular topic or issue)? In small groups think of examples either from your own experience or from that of someone you know. Be prepared to share your examples with the class as a whole. THE BENEFITS OF CRITICAL THINKING Having looked at some of the key intellectual standards governing critical reasoning (clarity, precision, and so forth), let’s now consider more specifically what you can expect to gain from a course in critical thinking. Critical Thinking in the Classroom When they first enter college, students are sometimes surprised to discover that their professors seem less interested in how they got their beliefs than they are in whether those beliefs can withstand critical scrutiny. In college the focus is on higher-order thinking: the active, intelligent evaluation of ideas and information. For this reason critical thinking plays a vital role throughout the The main aim of college curriculum. education is prac- In a critical thinking course, students learn a variety of skills that can tical and reflective greatly improve their classroom performance. These skills include judgment, a mind understanding the arguments and beliefs of others trained to be critically evaluating those arguments and beliefs critical everywhere developing and defending one’s own well-supported arguments and in the use of evi- beliefs dence. —Brand Blanchard Let’s look briefly at each of these three skills. bas07437_ch01_001-028.indd 7 11/24/09 8:00:17 AM  8 CHAPTER 1 Introduction to Critical Thinking Doonesbury © G. B. Trudeau. Reprinted with permission of Universal Press Syndicate. All rights reserved. To succeed in college, you must, of course, be able to understand the ma- terial you are studying. A course in critical thinking cannot make inherently difficult material easy to grasp, but critical thinking does teach a variety of skills that, with practice, can significantly improve your ability to understand the arguments and issues discussed in your college textbooks and classes. bas07437_ch01_001-028.indd 8 11/24/09 8:00:17 AM  The Benefits of Critical Thinking 9 In addition, critical thinking can help you critically evaluate what you are learning in class. During your college career, your instructors will often ask We don’t want you to discuss “critically” some argument or idea introduced in class. Critical you to axiom- thinking teaches a wide range of strategies and skills that can greatly improve atically accept your ability to engage in such critical evaluations. the conventional You will also be asked to develop your own arguments on particular topics wisdom on a or issues. In an American Government class, for example, you might be asked particular subject. to write a paper addressing the issue of whether Congress has gone too far Indeed, your first in restricting presidential war powers. To write such a paper successfully, you instinct should be must do more than simply find and assess relevant arguments and information. to question it. You must also be able to marshal arguments and evidence in a way that con- —John J. vincingly supports your view. The systematic training provided in a course in Mearsheimer critical thinking can greatly improve that skill as well. Critical Thinking in the Workplace Surveys indicate that fewer than half of today’s college graduates can expect to be working in their major field of study within five years of graduation. There is nothing This statistic speaks volumes about changing workplace realities. Increasingly, more practical employers are looking not for employees with highly specialized career skills, than sound since such skills can usually best be learned on the job, but for employees with thinking. good thinking and communication skills—quick learners who can solve prob- —Foundation for Critical Thinking lems, think creatively, gather and analyze information, draw appropriate con- clusions from data, and communicate their ideas clearly and effectively. These are exactly the kinds of generalized thinking and problem-solving skills that a course in critical thinking aims to improve. Critical Thinking in Life Critical thinking is valuable in many contexts outside the classroom and the workplace. Let’s look briefly at three ways in which this is the case. First, critical thinking can help us avoid making foolish personal decisions. All of us have at one time or another made decisions about consumer purchases, relationships, personal behavior, and the like that we later realized were seriously misguided or irrational. Critical thinking can help us avoid such mistakes by teach- ing us to think about important life decisions more carefully, clearly, and logically. Second, critical thinking plays a vital role in promoting democratic pro- cesses. Despite what cynics might say, in a democracy it really is “we the people” who have the ultimate say over who governs and for what purposes. It is vital, therefore, that citizens’ decisions be as informed and as deliberate as possible. Many of today’s most serious societal problems—environmental destruction, nuclear proliferation, religious and ethnic intolerance, decaying inner cities, failing schools, spiraling health-care costs, to mention just a few—have largely been caused by poor critical thinking. And as Albert Einstein once remarked, “The significant problems we face cannot be solved at the level of thinking we were at when we created them.” bas07437_ch01_001-028.indd 9 11/24/09 8:00:21 AM  10 CHAPTER 1 Introduction to Critical Thinking Third, critical thinking is worth studying for its own sake, simply for the Citizens who personal enrichment it can bring to our lives. One of the most basic truths of think for them- the human condition is that most people, most of the time, believe what they selves, rather than are told. Throughout most of recorded history, people accepted without ques- uncritically ingest- tion that the earth was the center of the universe, that demons cause disease, ing what their that slavery was just, and that women are inferior to men. Critical thinking, leaders tell them, honestly and courageously pursued, can help free us from the unexamined are the absolutely assumptions and biases of our upbringing and our society. It lets us step back necessary ingredi- from the prevailing customs and ideologies of our culture and ask, “This is ent of a society what I’ve been taught, but is it true? In short, critical thinking allows us to lead that is to remain self-directed, “examined” lives. Such personal liberation is, as the word itself truly free. implies, the ultimate goal of a liberal arts education. Whatever other benefits it —Howard Kahane brings, a liberal education can have no greater reward. BARRIERS TO CRITICAL THINKING The preceding section raises an obvious question: If critical thinking is so important, why is it that uncritical thinking is so common? Why is it that so many people—including many highly educated and intelligent people—find critical thinking so difficult? The reasons, as you might expect, are quite complex. Here is a list of some of the most common barriers to critical thinking: lack of relevant background information poor reading skills bias prejudice superstition egocentrism (self-centered thinking) sociocentrism (group-centered thinking) peer pressure conformism provincialism narrow-mindedness closed-mindedness distrust in reason relativistic thinking stereotyping unwarranted assumptions scapegoating rationalization bas07437_ch01_001-028.indd 10 11/24/09 8:00:21 AM  Barriers to Critical Thinking 11 denial wishful thinking short-term thinking selective perception selective memory overpowering emotions self-deception face-saving fear of change Let’s examine in detail five of these impediments—egocentrism, sociocen- trism, unwarranted assumptions, relativistic thinking, and wishful thinking— that play an especially powerful role in hindering critical thinking. Egocentrism Egocentrism is the tendency to see reality as centered on oneself. Egocentrics are selfish, self-absorbed people who view their interests, ideas, and values as superior to everyone else’s. All of us are affected to some degree by egocentric biases. Egocentrism can manifest itself in a variety of ways. Two common forms are self-interested thinking and self-serving bias. Self-interested thinking is the tendency to accept and defend beliefs that harmonize with one’s self-interest. Almost no one is immune to self-interested How quick come thinking. Most doctors support legislation making it more difficult for them the reasons for to be sued for malpractice; most lawyers do not. Most state university profes- approving what sors strongly support tenure, paid sabbaticals, low teaching loads, and a strong we like! faculty voice in university governance; many state taxpayers and university —Jane Austen administrators do not. Most factory workers support laws requiring advance notice of plant closings; most factory owners do not. Most American voters favor campaign finance reform; most elected politicians do not. Of course, some of these beliefs may be supported by good reasons. From a psychologi- cal standpoint, however, it is likely that self-interest plays at least some role in shaping the respective attitudes and beliefs. Self-interested thinking, however understandable it may seem, is a major obstacle to critical thinking. Everyone finds it tempting at times to reason Admit your that “this benefits me, therefore it must be good”; but from a critical thinking faults. I would if standpoint, such “reasoning” is a sham. Implicit in such thinking is the assump- I had any. tion that “What is most important is what I want and need.” But why should —Milton Berle I, or anyone else, accept such an arbitrary and obviously self-serving assump- tion? What makes your wants and needs more important than everyone else’s? Critical thinking condemns such special pleading. It demands that we weigh evidence and arguments objectively and impartially. Ultimately, it demands that we revere truth—even when it hurts. bas07437_ch01_001-028.indd 11 11/24/09 8:00:21 AM  12 CHAPTER 1 Introduction to Critical Thinking CALVIN AND HOBBES © Watterson. Reprinted with permission of Universal Press Syndicate. All rights reserved. Self-serving bias is the tendency to overrate oneself—to see oneself as The one thing better in some respect than one actually is. We have all known braggarts or that unites all know-it-alls who claim to be more talented or knowledgeable than they really human beings, are. If you are like most people, you probably think of yourself as being an un- regardless of age, usually self-aware person who is largely immune from any such self-deception. gender, religion, If so, then you too are probably suffering from self-serving bias. economic status, Studies show that self-serving bias is an extremely common trait. In one sur- or ethnic back- vey one million high school seniors were asked to rate themselves on their “ability ground, is that, to get along with others.” Not a single respondent rated himself below average in such deep down inside, ability.9 Other surveys have shown that 90 percent of business managers and more we all believe that than 90 percent of college professors rate their performance as better than average. we are above- It is easy, of course, to understand why people tend to overrate themselves.We all average drivers. like to feel good about ourselves. Nobody likes to think of himself or herself as —Dave Barry being “below average” in some important respect. At the same time, however, it is important to be able to look honestly at our personal strengths and weaknesses. We want to set high personal goals, but not goals that are wildly unrealistic. Self- confidence grounded in genuine accomplishment is an important element of suc- cess. Overconfidence is an obstacle to genuine personal and intellectual growth. E XERCISE 1.2 Are you overconfident in your beliefs? Here’s a simple test to determine if you are. For each of the following ten items, provide a low and a high guess such that you are 90 percent sure the correct answer falls between the two.Your challenge is to be neither too narrow (i.e., overconfident) nor too wide (i.e., underconfident). If you successfully meet the challenge, you should have 10 percent misses—that is, exactly one miss.10 bas07437_ch01_001-028.indd 12 11/24/09 8:00:21 AM  Barriers to Critical Thinking 13 90% Confidence Range LOW HIGH 1. Martin Luther King’s age at death __________ __________ 2. Length of Nile River (in miles) __________ __________ 3. Percentage of African Americans in the United States __________ __________ 4. Number of books in the Old Testament __________ __________ 5. Diameter of the moon (in miles) __________ __________ 6. Weight of an empty Boeing 747 (in pounds) __________ __________ 7. Current population of California __________ __________ 8. Year in which Wolfgang Amadeus He who knows Mozart was born __________ __________ most, knows 9. Air distance from London to Tokyo best how little he (in miles) __________ __________ knows. —Thomas 10. Deepest known point in the ocean Jefferson (in feet) __________ __________11 Sociocentrism Sociocentrism is group-centered thinking. Just as egocentrism can hinder ra- tional thinking by focusing excessively on the self, so sociocentrism can hinder rational thinking by focusing excessively on the group. Sociocentrism can distort critical thinking in many ways. Two of the most important are group bias and conformism. Group bias is the tendency to see one’s own group (nation, tribe, sect, peer group, and the like) as being inherently better than others. Social scientists Custom and tell us that such thinking is extremely common throughout human history and example have across cultures. Just as we seem naturally inclined to hold inflated views of our- a much more selves, so we find it easy to hold inflated views of our family, our community, persuasive power or our nation. Conversely, we find it easy to look with suspicion or disfavor on than any certitude those we regard as “outsiders.” obtained by way Most people absorb group bias unconsciously, usually from early child- of inquiry. hood. It is common, for example, for people to grow up thinking that their —René Descartes society’s beliefs, institutions, and values are better than those of other societ- ies. Consider this exchange between eight-year-old Maurice D. and the well- known Swiss scientist and philosopher Jean Piaget: Maurice D. (8 years, 3 months old): If you didn’t have any nationality and you were given a free choice of nationality, which would you choose? Swiss nationality. Why? Because I was born in Switzerland. Now look, do you think the French and bas07437_ch01_001-028.indd 13 11/24/09 8:00:22 AM  14 CHAPTER 1 Introduction to Critical Thinking Pop Culture Connection Poker and Critical Thinking Poker players fall victim to critical thinking barriers like wishful think- ing and self-serving bias just like anybody else.12 One barrier that can be particularly costly to poker players is overconfidence. Overconfi- dent players think that they’re better, or luckier, than they actually are. This often leads them to play with far superior opponents, to stay in too many hands, and to bet recklessly. The result: Players who overrate their abilities quickly become ATMs for their tablemates. Poker legend Doyle Brunson tells a cautionary tale about the dan- gers of overconfidence. A cocky New Yorker calling himself “Roches- ter Ricky” and flashing a big bankroll walked into a Fort Worth poker parlor. Around the table sat Amarillo Slim, Puggy Pearson, Johnny Moss, Sailor Roberts, Brunson himself, and a couple of Texas busi- nessmen. Two things quickly became apparent. Though he knew his game, Rochester hadn’t played much no-limit poker, and he hadn’t a clue he was playing against some of the best no-limit Hold’em poker talent in the world. Rochester didn’t realize that strategies that work well in limit games (for example, calling frequently and bluffing cautiously) often backfire in no-limit games. His parting words as he gathered up the paltry remnants of his $10,000 bankroll were “If you guys are ever in Rochester, don’t bother to look me up. You won’t see me playing Hold’em against Texans as long as I live.”13 As the great American philosopher Clint Eastwood said, “A man’s got to know his limitations.” the Swiss are equally nice, or the one nicer or less nice than the other? The Swiss are nicer. Why? The French are always nasty. Who is more intelligent, the Swiss or the French, or do you think they’re just the same? The Swiss are more intelligent. Why? Because they learn French quickly. If I asked a French boy to choose any nationality he liked, what country do you think he’d choose? He’d choose France. Why? Because he was born in France. And what would he say about who’s nicer? Would he think To those who the Swiss and the French equally nice or one better than the other? He’d say the would investigate French are nicer. Why? Because he was born in France. And who would he think more the cause of exist- intelligent? The French. Why? He’d say that the French want to learn quicker than the Swiss. Now you and the French boy don’t really give the same answer. Who do ing opinions, the you think answered best? I did. Why? Because Switzerland is always better.14 study of predis- positions is much Although most people outgrow such childish nationalistic biases to some more important extent, few of us manage to outgrow them completely. Clearly, this kind of than the study of “mine-is-better” thinking lies at the root of a great deal of human conflict, argument. intolerance, and oppression. —W. E. H. Lecky Conformism refers to our tendency to follow the crowd—that is, to conform (often unthinkingly) to authority or to group standards of conduct bas07437_ch01_001-028.indd 14 11/24/09 8:00:22 AM  Barriers to Critical Thinking 15 and belief. The desire to belong, to be part of the in-group, can be among the most powerful of human motivations. As two classic experiments demonstrate, this desire to conform can seriously cripple our powers of critical reasoning and decision making. In the first experiment, conducted in the 1950s by Solomon Asch, groups of eight college students were asked to match a standard line like the following with three comparison lines such as these: A B C In each group, only one of the eight participants was unaware of the true na- ture of the experiment; the other seven were confederates working in league When fifty million with the experimenter. In each case the single true subject was seated at the people say a fool- end of the table and asked to answer last. In some trials the seven confederates ish thing it is still unanimously gave the correct answer (B); in others they unanimously gave a foolish thing. an incorrect answer. The results: When no pressure to conform was present, —Anatole France subjects gave the correct answer more than 99 percent of the time. When faced with the united opposition of their peers, however, almost one-third (32 percent) of the subjects refused to believe their own eyes and gave answers that were obviously incorrect! Another famous experiment was conducted by Stanley Milgram in the 1960s.15 In Milgram’s experiment, subjects were asked to administer a series of When all think increasingly severe electrical shocks to people whom the subjects could hear alike, then no one but couldn’t see. (In fact, no actual shocks were given; the shock “victims” were is thinking. actually confederates who merely pretended to be in pain.) Subjects were told —Walter Lippmann that they were participating in a study of the effects of punishment on learn- ing.Their task was to act as “teachers” who inflicted progressively more painful shocks on “learners” whenever the latter failed to answer a question correctly. The severity of the shocks was controlled by a series of thirty switches, which ranged in 15-volt intervals from 15 volts (“Slight Shock”) to 450 volts (“XX Danger: Severe Shock”). The purpose of the study was to determine how far ordinary people would go in inflicting pain on total strangers, simply because they were asked to do so by someone perceived to be “an authority.” The results were, well, shocking. More than 85 percent of the subjects continued to administer shocks beyond the 300-volt mark, long after the point at which they could hear the victims crying out or pounding on the walls in pain. After the 330-volt mark, the screaming stopped, and for all the subjects knew, the victims were either unconscious or dead. Despite that, nearly two- thirds (65 percent) of the subjects continued to administer shocks, as they were instructed, until they had administered the maximum 450 volts. The lesson of these studies is clear: “Authority moves us. We are im- Man is born to pressed, influenced, and intimidated by authority, so much so that, under the think for himself. right conditions, we abandon our own values, beliefs, and judgments, even —Denis Diderot doubt our own immediate sensory experience.”16 As critical thinkers, we need bas07437_ch01_001-028.indd 15 11/24/09 8:00:22 AM  16 CHAPTER 1 Introduction to Critical Thinking to be aware of the seductive power of peer pressure and reliance on authority and develop habits of independent thinking to combat them. Unwarranted Assumptions and Stereotypes An assumption is something we take for granted, something we believe to be true without any proof or conclusive evidence. Almost everything we think and do is based on assumptions. If the weather report calls for rain, we take an umbrella because we assume that the meteorologist is not lying, that the report is based on a scientific analysis of weather patterns, that the instruments are accurate, and so forth. There may be no proof that any of this is true, but we realize that it is wiser to take the umbrella than to insist that the weather bureau provide exhaustive evidence to justify its prediction. Although we often hear the injunction “Don’t assume,” it would be im- possible to get through a day without making assumptions; in fact, many of our daily actions are based on assumptions we have drawn from the patterns in our experience.You go to class at the scheduled time because you assume that class is being held at its normal hour and in its same place. You don’t call the professor each day to ask if class is being held; you just assume that it is. Such assumptions are warranted, which means that we have good reason to hold them. When you see a driver coming toward you with the turn signal on, you have good reason to believe that the driver intends to turn.You may be incor- rect, and it might be safer to withhold action until you are certain, but your assumption is not unreasonable. Unwarranted assumptions, however, are unreasonable. An unwarranted as- sumption is something taken for granted without good reason. Such assump