A Guide to Critical Thinking


A Guide to Critical Thinking

A Guide to Critical Thinking


With Good Reason: A Guide to Critical Thinking

Christopher Foster Ashford University

James Hardy Ashford University

Gloria Zúñiga y Postigo Ashford University

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James Hardy, Christopher Foster, and Gloria Zúñiga y Postigo

With Good Reason: A Guide to Critical Thinking

Editor in Chief, AVP: Steve Wainwright

Executive Editor: Anna Lustig

Development Editor: Rebecca Paynter

Assistant Editor: Jessica Sarra

Editorial Assistant: Lukas Schulze

Production Editor: Catherine Morris

Media Production: Amanda Nixon, LSF Editorial

Copy Editor: Lauri Scherer, LSF Editorial

Photo Researcher: Amanda Nixon, LSF Editorial

Cover Design: Bambang Suparman Ibrahim

Printing Services: Bordeaux

Production Services: Lachina. A Guide to Critical Thinking

Permission Editor: D’Stair Permissions Agency

Cover Image: juuce/iStock and espiegle/iStock

ISBN-10: 1621785661

ISBN-13: 978-1-62178-566-8

Copyright © 2015 Bridgepoint Education, Inc.

All rights reserved.

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Brief Contents

Chapter 1: An Introduction to Critical Thinking and Logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Chapter 2: The Argument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Chapter 3: Deductive Reasoning . . . . . . . . . . . . . . . . . . . . . . . . .59

Chapter 4: Propositional Logic . . . . . . . . . . . . . . . . . . . . . . . . 119

Chapter 5: Inductive Reasoning . . . . . . . . . . . . . . . . . . . . . . . 165

Chapter 6: Deduction and Induction: Putting It All Together . . . . . . . . . . . . . . . . . . . . . . 207

Chapter 7: Informal Fallacies . . . . . . . . . . . . . . . . . . . . . . . . . . 239

Chapter 8: Persuasion and Rhetoric . . . . . . . . . . . . . . . . . . . 279

Chapter 9: Logic in Real Life . . . . . . . . . . . . . . . . . . . . . . . . . . . 319

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

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About the Authors xiii Acknowledgments xv Preface xvii

Chapter 1 An Introduction to Critical Thinking and Logic 1

1 .1 What Is Critical Thinking? 2 The Importance of Critical Thinking 3 Becoming a Critical Thinker 6

1 .2 Three Misconceptions About Logic 7 Logic Is for Robots 7 Logic Does Not Need to Be Learned 9 Logic Is Too Hard 10

1 .3 What Is Logic? 11 The Study of Arguments 11 A Tool for Arriving at Warranted Judgments 12 Formal Versus Informal Logic 14

1 .4 Arguments Outside of Logic 14 Arguments in Ordinary Language 14 Rhetorical Arguments 15 Revisiting Arguments in Logic 16

1 .5 The Importance of Language in Logic 17

1 .6 Logic and Philosophy 19 The Goal of Philosophy 20 Philosophy and Logical Reasoning 20

Summary and Resources 21


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Chapter 2 The Argument 25

2 .1 Arguments in Logic 26 Claims 29 The Standard Argument Form 31

2 .2 Putting Arguments in the Standard Form 33 Find the Conclusion First 34 Find the Premises Next 36 The Necessity of Paraphrasing 38 Thinking Analytically 39

2 .3 Representing Arguments Graphically 42 Representing Reasons That Support a Conclusion 42 Representing Counterarguments 45 Diagramming Efficiently 46

2 .4 Classifying Arguments 47 Deductive Arguments 48 Inductive Arguments 49 Arguments Versus Explanations 50

Summary and Resources 53

Chapter 3 Deductive Reasoning 59

3 .1 Basic Concepts in Deductive Reasoning 60 Validity 60 Soundness 62 Deduction 63

3 .2 Evaluating Deductive Arguments 66 Representing Logical Form 66 Using the Counterexample Method 68

3 .3 Types of Deductive Arguments 70 Mathematical Arguments 70 Arguments From Definitions 71 Categorical Arguments 72 Propositional Arguments 72

3 .4 Categorical Logic: Introducing Categorical Statements 73 Clarifying Particular Statements 76


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Clarifying Universal Statements 76 Accounting for Conversational Implication 78

3 .5 Categorical Logic: Venn Diagrams as Pictures of Meaning 80 Drawing Venn Diagrams 81 Drawing Immediate Inferences 84

3 .6 Categorical Logic: Categorical Syllogisms 91 Terms 91 Distribution 91 Rules for Validity 93 Venn Diagram Tests for Validity 94

3 .7 Categorical Logic: Types of Categorical Arguments 111 Sorites 111 Enthymemes 112 Validity in Complex Arguments 113

Summary and Resources 115

Chapter 4 Propositional Logic 119

4 .1 Basic Concepts in Propositional Logic 120 The Value of Formal Logic 121 Statement Forms 122

4 .2 Logical Operators 123 Conjunction 124 Disjunction 126 Negation 128 Conditional 129

4 .3 Symbolizing Complex Statements 133 Truth Tables With Complex Statements 135 Truth Tables With Three Letters 137

4 .4 Using Truth Tables to Test for Validity 140 Examples With Arguments With Two Letters 141 Examples With Arguments With Three Letters 144

4 .5 Some Famous Propositional Argument Forms 149 Common Valid Forms 149 Common Invalid Forms 152

Summary and Resources 158

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Chapter 5 Inductive Reasoning 165

5 .1 Basic Concepts in Inductive Reasoning 166 Inductive Strength 167 Inductive Cogency 170 A Guide to Critical Thinking

5 .2 Statistical Arguments: Statistical Syllogisms 171 Form 172 Weak Statistical Syllogisms 173

5 .3 Statistical Arguments: Inductive Generalizations 174 Representativeness 175 Confidence Level 179 Applying This Knowledge 180

5 .4 Causal Relationships: The Meaning of Cause 181 Sufficient Conditions 181 Necessary Conditions 182 Necessary and Sufficient Conditions 183 Other Types of Causes 184 Correlational Relationships 184 A Guide to Critical Thinking

5 .5 Causal Arguments: Mill’s Methods 186 Method of Agreement 187 Method of Difference 188 Joint Method of Agreement and Difference 189 Method of Concomitant Variation 190

5 .6 Arguments From Authority 192

5 .7 Arguments From Analogy 193 Evaluating Arguments From Analogy 194 Analogies in Moral Reasoning 197 Other Uses of Analogies 198

Summary and Resources 203

Chapter 6 Deduction and Induction: Putting It All Together 207

6 .1 Contrasting Deduction and Induction 208

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6 .2 Choosing Between Induction and Deduction 211 Availability 211 Robustness 212 Persuasiveness 214

6 .3 Combining Induction and Deduction 216

6 .4 Reasoning About Science: The Hypothetico–Deductive Method 218 Step 1: Formulate a Hypothesis 219 Step 2: Deduce a Consequence From the Hypothesis 219 Step 3: Test Whether the Consequence Occurs 220 Step 4: Reject the Hypothesis If the Consequence Does Not Occur 220

6 .5 Inference to the Best Explanation 225 Form 228 Virtue of Simplicity 229 How to Assess an Explanation 231 A Limitation 232

Summary and Resources 236

Chapter 7 Informal Fallacies 239

7 .1 Fallacies of Support 241 Begging the Question 241 Circular Reasoning 242 Hasty Generalizations and Biased Samples 243 Appeal to Ignorance and Shifting the Burden of Proof 245 Appeal to Inadequate Authority 246 False Dilemma 248 False Cause 249

7 .2 Fallacies of Relevance 251 Red Herring and Non Sequitur 251 Appeal to Emotion 252 Appeal to Popular Opinion 255 Appeal to Tradition 256 Ad Hominem and Poisoning the Well 257

7 .3 Fallacies of Clarity 261 The Slippery Slope 261 Equivocations 262 The Straw Man 264

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Fallacy of Accident 267 Fallacies of Composition and Division 268

Summary and Resources 273

Chapter 8 Persuasion and Rhetoric 279

8 .1 Obstacles to Critical Thinking: The Self 280 Stereotypes 280 Cognitive Biases 282

8 .2 Obstacles to Critical Thinking: Rhetorical Devices 289 Weasel Words 290 Euphemisms and Dysphemisms 291 Proof Surrogates 293 Hyperbole 294 Innuendo and Paralipsis 295

8 .3 The Media and Mediated Information 300 Manipulating Images 301 Advertising 302 Other Types of Mediated Information 306

8 .4 Evaluating the Source: Who to Believe 308 Reputation and Authorship 309 Accuracy and Currency 312 Interested Parties 312

Summary and Resources 314

Chapter 9 Logic in Real Life 319

9 .1 The Argumentative Essay 320 The Problem 321 The Thesis 322 The Premises 323

9 .2 Strengthening the Argumentative Essay 327 Clarification and Support 327 The Objection 329 The Rebuttal 330 Closing Your Essay 331

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A Guide to Critical Thinking


9 .3 Practical Arguments: Building Arguments for Everyday Use 333 The Claim 333 The Data 334 The Warrant 334 Comparing the Models 335

9 .4 Confronting Disagreement 338 Applying the Principle of Accuracy 339 Applying the Principle of Charity 340 Balancing the Principles of Accuracy and Charity 341 Practicing Effective Criticism 342

9 .5 Case Study: Interpretation and Criticism in Practice 346 Examining the Initial Argument 347 Examining the Objection 347 Examining the Wording 348 Drawing a Conclusion 349

9 .6 Other Applications of Logic 349 Symbolic Logic 350 Computer Science 350 Artificial Intelligence 350 Engineering 351 Politics (Speech Writing) 351

Summary and Resources 351

Glossary 355

References 363

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James Hardy, Ashford University Dr. James Hardy is part of the core faculty of the Humanities & Science department at Ashford University. He obtained a PhD in philosophy from Indiana University, a master’s degree in philosophy from the University of Washington, and bachelor’s degrees in philosophy and psy- chology from Utah State University. He has taught philosophy at multiple universities since 1998 and has had the opportunity to teach across the general education spectrum, including courses in algebra, speech, English, and physics. Dr. Hardy’s favorite part of teaching is watch- ing students get excited about learning, helping them achieve their dreams, and seeing their excitement as new worlds of knowledge open up to them.

Dr. Hardy loves spending time outdoors hiking, backpacking, and canoeing—especially when he can do so with family members. He has lived all over the United States and has always found beauty and natural wonders wherever he has lived. The only time he is happier than when he is in nature is when he is spending time with his family.

Christopher Foster, Ashford University Dr. Christopher Foster is lead faculty of the Humanities & Science department at Ashford University. He holds a PhD in philosophy with a specialization in logic and language and a master’s degree in philosophy from the University of Kansas (KU). His undergraduate work was completed at the University of California–Davis, where he earned bachelor’s degrees in mathematics and philosophy. Dr. Foster began his career as a graduate teaching assistant at KU and went on to teach at Brigham Young University and Utah Valley University. Dr. Foster has a passion for philosophy and believes that digging deeply into life’s ultimate questions is often the best way to improve students’ critical thinking and writing skills. He lives in Orem, Utah, with his wife, Cherie, and two daughters, Avery and Adia.

Gloria Zúñiga y Postigo, Ashford University Dr. Gloria Zúñiga y Postigo is part of the core faculty of the Humanities & Science department at Ashford University. She earned a PhD in philosophy from the University at Buffalo, special- izing in ontology, ethics, and philosophy of economics. Her previous studies are in philosophy at the University of California–Berkeley and economics at California State University–East Bay. Dr. Zúñiga y Postigo’s present research interests include examinations of the effect in our experiences of moral, aesthetic, and economic phenomena; and value in the Brentano School, the Menger School, and the Göttingen Circle scholars. Teaching philosophy is one her greatest passions. She especially enjoys teaching informal logic, because it empowers students with a tool for distinguishing truth from the mere appearance of truth, thereby making it possible for them to achieve fulfilling lives with greater efficacy.

About the Authors

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The authors would like to acknowledge the people who made significant contributions to the development of this text: Anna Lustig, executive editor; Rebecca Paynter, development edi- tor; Jessica Sarra, assistant editor; Lukas Schulze, editorial assistant; Catherine Morris, pro- duction editor; Amanda Nixon, media production; and Lauri Scherer and LSF Editorial, copy editors. Additional thanks go to Justin Harrison and Marc Joseph for their work creating and accuracy checking the ancillary materials for this text.

The authors would also like to thank the following reviewers, as well as other anonymous reviewers, for their valuable feedback and insight:

Justin Harrison, Ashford University

Mark Hébert, Austin College

Marc Joseph, Mills College

Stephen Krogh, Ashford University

Renee Levant, Ashford University

Andrew Magrath, Kent State University

Zachary Martin, Florida State University

John McAteer, Ashford University

Bradley Thames, Ashford University

Finally, but not least importantly, the authors would like to acknowledge their respective spouses—Teresa Hardy, Cherie Farnes, and Jacob Arfwedson—for their loving understand- ing of the long hours that this project demanded, as well as all characters in popular culture (for example, Sherlock Holmes, Mr. Spock, and Dr. House) who have kept logic present in everyday conversations. The rewards of our work are enriched by the former and reassured by the latter. A Guide to Critical Thinking


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With Good Reason: A Guide to Critical Thinking examines the specific ways we use language to reason about things. The study of logic improves our ability to think. It forces us to pay closer attention to the way language is used (and misused). It helps make us better at providing good reasons for our decisions. With Good Reason: A Guide to Critical Thinking seeks to help you examine and develop these abilities in order to improve them and to avoid being per- suaded by the faulty reasoning of others.

Textbook Features With Good Reason: A Guide to Critical Thinking includes a number of features to help students understand key concepts and think critically:

Everyday Logic boxes give students the opportunity to see principles applied to a variety of real-world scenarios.

A Closer Look boxes give students the chance to explore more in-depth concepts and issues in critical thinking.

Figures illustrate a variety of concepts in easy-to-understand ways.

Practice Problems provide an opportunity for students to exercise the knowledge they have learned in each chapter.

Knowledge Checks test preconceptions about and comprehension of each chapter’s top- ics and lead to a personalized reading plan based on these results.

Moral of the Story boxes and Chapter Summaries review the key ideas and takeaways in each chapter.

Interactive Features in the e-book allow students to engage with the content on a more dynamic level. Animated scenarios in Logic in Action show students how logic might be used in real life. Consider This interactions invite students to think about various issues in more depth. Interactive exercises in Connecting the Dots give students further opportuni- ties to practice what they have learned.

Key Terms list and define important vocabulary discussed in the chapter, offering an opportunity for a final review of chapter concepts. In the e-book, students can click on the term to reveal the definition and quiz themselves in the process. A Guide to Critical Thinking


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1An Introduction to Critical Thinking and Logic

Hemera Technologies/Ablestock.com/Thinkstock

Learning Objectives After reading this chapter, you should be able to:

1. Explain the importance of critical thinking and logic.

2. Describe the relationship between critical thinking and logic.

3. Explain why logical reasoning is a natural human attribute that we all have to develop as a skill.

4. Identify logic as a subject matter applicable to many other disciplines and everyday life.

5. Distinguish the various uses of the word argument that do not pertain to logic.

6. Articulate the importance of language in logical reasoning.

7. Describe the connection between logic and philosophy.

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Section 1.1 What Is Critical Thinking?

This book will introduce you to the tools and practices of critical thinking. Since the main tool for critical thinking is logical reasoning, the better part of this book will be devoted to discuss- ing logic and how to use it effectively to become a critical thinker.

We will start by examining the practical importance of critical thinking and the virtues it requires us to nurture. Then we will explore what logic is and how the tools of logic can help us lead easier and happier lives. We will also briefly review a critical concept in logic—the argument—and discuss the importance of language in making good judgments. We will con- clude with a snapshot of the historical roots of logic in philosophy.

1.1 What Is Critical Thinking? What is critical thinking? What is a critical thinker? Why do you need a guide to think criti- cally? These are good questions, but ones that are seldom asked. Sometimes people are afraid to ask questions because they think that doing so will make them seem ignorant to others. But admitting you do not know something is actually the only way to learn new things and better understand what others are trying to tell you.

There are differing views about what critical thinking is. For the most part, people take bits and pieces of these views and carry on with their often imprecise—and sometimes conflicting— assumptions of what critical thinking may be. However, one of the ideas we will discuss in this book is the fundamental importance of seeking truth. To this end, let us unpack the term critical thinking to better understand its meaning.

First, the word thinking can describe any number of cognitive activities, and there is certainly more than one way to think. We can think analytically, creatively, strategically, and so on (Sousa, 2011). When we think analytically, we take the whole that we are examining—this could be a term, a situation, a scientific phenomenon—and attempt to identify its components. The next step is to examine each component individually and understand how it fits with the other com- ponents. For example, we are currently examining the meaning of each of the words in the term critical thinking so we can have a better understanding of what they mean together as a whole.

Analytical thinking is the kind of thinking mostly used in academia, science, and law (includ- ing crime scene investigation). In ordinary life, however, you engage in analytical thinking more often than you imagine. For example, think of a time when you felt puzzled by some- one else’s comment. You might have tried to recall the original situation and then parsed out the language employed, the context, the mood of the speaker, and the subject of the com- ment. Identifying the different parts and looking at how each is related to the other, and how together they contribute to the whole, is an act of analytical thinking.

When we think creatively, we are not focused on relationships between parts and their wholes, as we are when we think analytically. Rather, we try to free our minds from any boundaries such as rules or conventions. Instead, our tools are imagination and innovation. Suppose you are cooking, and you do not have all the ingredients called for in your recipe. If you start thinking creatively, you will begin to look for things in your refrigerator and pantry that can substitute for the missing ingredients. But in order to do this, you must let go of the recipe’s expected outcome and conceive of a new direction.

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Section 1.1 What Is Critical Thinking?

When we think strategically, our focus is to first lay out a master plan of action and then break it down into smaller goals that are organized in such a way as to support our outcomes. For exam- ple, undertaking a job search involves strategic planning. You must identify due dates for applications, request let- ters of recommendations, prepare your résumé and cover letters, and so on. Thinking strategically likely extends to many activities in your life, whether you are going grocery shopping or planning a wedding.

What, then, does it mean to think criti- cally? In this case the word critical has nothing to do with criticizing others in a negative way or being surly or cynical.

Rather, it refers to the habit of carefully evaluating ideas and beliefs, both those we hear from others and those we formulate on our own, and only accepting those that meet certain stan- dards. While critical thinking can be viewed from a number of different perspectives, we will define critical thinking as the activity of careful assessment and self-assessment in the process of forming judgments. This means that when we think critically, we become the vigilant guard- ians of the quality of our thinking.

Simply put, the “critical” in critical thinking refers to a healthy dose of suspicion. This means that critical thinkers do not simply accept what they read or hear from others—even if the information comes from loved ones or is accompanied by plausible-sounding statistics. Instead, critical thinkers check the sources of information. If none are given or the sources are weak or unreliable, they research the information for themselves. Perhaps most importantly, critical thinkers are guided by logical reasoning.

As a critical thinker, always ask yourself what is unclear, not understood, or unknown. This is the first step in critical thinking because you cannot make good judgments about things that you do not understand or know.

The Importance of Critical Thinking Why should you care about critical thinking? What can it offer you? Suppose you must make an important decision—about your future career, the person with whom you might want to spend the rest of your life, your financial investments, or some other critical matter. What considerations might come to mind? Perhaps you would wonder whether you need to think about it at all or whether you should just, as the old saying goes, “follow your heart.” In doing so, you are already clarifying the nature of your decision: purely rational, purely emotional, or a combination of both.


Critical thinking involves carefully assessing information and its sources.

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Section 1.1 What Is Critical Thinking?

In following this process you are already starting to think critically. First you started by asking questions. Once you examine the answers, you would then assess whether this information is sufficient, and perhaps proceed to research further information from reli- able sources. Note that in all of these steps, you are making distinctions: You would distinguish between relevant and irrelevant questions, and from the relevant questions, you would distin- guish the clear and precise ones from the others. You also would distinguish the answers that are helpful from those that are not. And finally, you would separate out the good sources for your research, leaving aside the weak and biased ones.

Making distinctions also determines the path that your examination will follow, and herein lies the connection between critical thinking and logic. If you decide you should examine the best reasons that support each of the possible options available, then this choice takes you in the direction of logic. One part of logical reasoning is the weighing of evidence. When making an important decision, you will need to identify which factors you consider favorable and which you consider unfavorable. You can then see which option has the strongest evidence in its favor (see Everyday Logic: Evidence, Beliefs, and Good Thinking for a discussion of the importance of evidence).

Consider the following scenario. You are 1 year away from graduating with a degree in busi- ness. However, you have a nagging feeling that you are not cut out for business. Based on your research, a business major is practical and can lead to many possibilities for well-paid employment. But you have discovered that you do not enjoy the application or the analysis of quantitative methods—something that seems to be central to most jobs in business. What should you do?

Many would seek advice from trusted people in their lives—people who know them well and thus theoretically might suggest the best option for them. But even those closest to us can offer conflicting advice. A practical parent may point out that it would be wasteful and possibly risky to switch to another major with only 1 more year to go. A reflective friend may point out that the years spent studying business could be considered simply part of a journey of self-discovery, an investment of time that warded off years of unhappiness after gradua- tion. In these types of situations, critical thinking and logical reasoning can help you sort out competing considerations and avoid making a haphazard decision.

We all find ourselves at a crossroads at various times in our lives, and whatever path we choose will determine the direction our lives will take. Some rely on their emotions to help them make their decisions. Granted, it is difficult to deny the power of emotions. We recall more vividly those moments or things in our lives that have had the strongest emotional


Can you recall a time when you acted or made a decision while you were experiencing strong emotions? Relying on our emotions to make decisions undermines our ability to develop confidence in our rational judgments. Moreover, emotional decisions cannot typically be justified and often lead to regret.

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Section 1.1 What Is Critical Thinking?

impact: a favorite toy, a first love, a painful loss. Many interpret gut feelings as revelations of what they need to do. It is thus easy to assume that emotions can lead us to truth. Indeed, emotions can reveal phenomena that may be otherwise inaccessible. Empathy, for example, permits us to share or recognize the emotions that others are experiencing (Stein, 1989).

The problem is that, on their own, emotions are not reliable sources of information. Emotions can lead you only toward what feels right or what feels wrong—but cannot guarantee that what feels right or wrong is indeed the right or wrong thing to do. For example, acting self- ishly, stealing, and lying are all actions that can bring about good feelings because they satisfy our self-serving interests. By contrast, asking for forgiveness or forgiving someone can feel wrong because these actions can unleash feelings of embarrassment, humiliation, and vulner- ability. Sometimes emotions can work against our best interests. For example, we are often fooled by false displays of goodwill and even affection, and we often fall for the emotional appeal of a politician’s rhetoric.

The best alternative is the route marked by logical reasoning, the principal tool for developing critical thinking. The purpose of this book is to help you learn this valuable tool. You may be wondering, “What’s in it for me?” For starters, you are bound to gain the peace of mind that comes from knowing that your decisions are not based solely on a whim or a feeling but have the support of the firmer ground of reason. Despite the compelling nature of your own emo- tional barometer, you may always wonder whether you made the right choice, and you may not find out until it is too late. Moreover, the emotional route for decision making will not help you develop confidence in your own judgments in the face of uncertainty.

In contrast, armed with the skill of logical reasoning, you can lead a life that you choose and not a life that just happens to you. This power alone can make the difference between a happy and an unhappy life. Mastering critical thinking results in practical gains—such as the ability to defend your views without feeling intimidated or inadequate and to protect yourself from manipulation or deception. This is what’s in it for you, and this is only the beginning.

Everyday Logic: Evidence, Beliefs, and Good Thinking

It is wrong always, everywhere, and for anyone to believe anything on insufficient evidence. —W. K. Clifford (1879, p. 186)

British philosopher and mathematician W. K. Clifford’s claim—that it is unethical to believe anything if you do not have sufficient evidence for it—elicited a pronounced response from the philosophical community. Many argued that Clifford’s claim was too strong and that it is acceptable to believe things for which we lack the requisite evidence. Whether or not one absolutely agrees with Clifford, he raises a good point. Every day, millions of people make deci- sions based on insufficient evidence. They claim that things are true or false without putting in the time, effort, and research necessary to make those claims with justification.

You have probably witnessed an argument in which people continue to make the same claims until they either begin to become upset or merely continue to restate their positions without adding anything new to the discussion. These situations often devolve and end with state- ments such as, “Well, I guess we will just agree to disagree” or “You are entitled to your opin- ion, and I am entitled to mine, and we will just have to leave it at that.” However, upon further reflection we have to ask ourselves, “Are people really entitled to have any opinion they want?”


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Section 1.1 What Is Critical Thinking?

From the perspective of critical thinking, the answer is no. Although people are legally entitled to their beliefs and opinions, it would be intellectually irresponsible of them to feel entitled to an opinion that is unsupported by logical reasoning and evidence; people making this claim are conflating freedom of speech with freedom of opinion. A simple example will illustrate this point. Suppose someone believes that the moon is composed of green cheese. Although he is legally entitled to his belief that the moon is made of green cheese, he is not rationally entitled to that belief, since there are many reasons to believe and much evidence to show that the moon is not composed of green cheese.

Good thinkers constantly question their beliefs and examine multiple sources of evidence to ensure their beliefs are true. Of course, people often hold beliefs that seem warranted but are later found not to be true, such as that the earth is flat, that it is acceptable to paint baby cribs with lead paint, and so on. However, a good thinker is one who is willing to change his or her views when those views are proved to be false. There are certain criteria that must be met for us to claim that someone is entitled to a specific opinion or position on an issue.

There are other examples where the distinction is not so clear. For instance, some people believe that women should be subservient to men. They hold this belief for many reasons, but the pre- dominant one is because specific religions claim this is the case. Does the fact that a religious text claims that women should serve men provide sufficient evidence for one to believe this claim? Many people believe it does not. However, many who interpret their religious texts in this man- ner would claim that these texts do provide sufficient evidence for such claims.

It is here that we see the danger and difficulty of providing hard-and-fast definitions of what constitutes sufficient evidence. If we believe that written words in books came directly from divine sources, then we would be prone to give those words the highest credibility in terms of the strength of their evidence. However, if we view written words as arguments presented by their authors, then we would analyze the text based on the evidence and reasoning presented. In the latter case we would find that these people are wrong and that they are merely making claims based on their cultural, male-dominated environments.

Of course, all people have the freedom to believe what they want. However, if we think of entitlement as justification, then we cannot say that all people are entitled to their opinions and beliefs. As you read this book, think about what you believe and why. If you do not have reasons or supporting evidence for your beliefs and opinions, you should attempt to find it. Try not to get sucked into arguments without having evidence. Most important, as a good thinker, you should be willing and able to admit the strengths and weaknesses of various posi- tions on issues, especially your own. At the same time, if in your search for evidence you find that the opposing position is the stronger one, you should be willing to change your position. It is also a sign of good thinking to suspend judgment when you suspect that the arguments of others are not supported by evidence or logical reasoning. Suspending judgment can protect you from error and making rash decisions that lead to negative outcomes.

Everyday Logic: Evidence, Beliefs, and Good Thinking (continued)

Becoming a Critical Thinker By now it should be clear that critical thinking is an important life skill, one that will have a decisive impact on our lives. It does not take luck or a genetic disposition to be a critical thinker. Anyone can master critical thinking skills. So how do you become a critical thinker? Earlier in

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Section 1.2 Three Misconceptions About Logic

the chapter, logical reasoning was described as the main tool for critical thinking. Thus, the most fundamental step in becoming a critical thinker is to recognize the importance of reason as the filter for your beliefs and actions. Once you have done this, you will be in the right frame of mind to start learning about logic and identify what tools of logic are at your disposal.

It is also important to note that becoming a critical thinker demands intellectual modesty. We can understand intellectual modesty as the willingness to put our egos in check because we see truth seeking as a far greater and more satisfying good than seeking to be right. Critical thinkers do not care about seeking approval by trying to show that they are right. They do not assume that disagreement reflects a lack of intelligence or insight. Being intellectually modest means recognizing not only that we can make mistakes, but also that we have much to learn. If we are (a) aware that we are bound to make mistakes and that we will benefit when we recognize them; (b) willing to break old habits and embrace change; and, perhaps most importantly, (c) genuinely willing to know what others think, then we can be truly free to experience life as richly and satisfactorily as a human being can.

1.2 Three Misconceptions About Logic If logic is so important to critical thinking, we must of course examine what logic is. This task is not as easy as it sounds, and before we tackle it we must first dismantle some common misconceptions about the subject.

Logic Is for Robots The first misconception is that it is not normal for humans to display a command of logic. (In fact, some suggest that humans created, rather than discovered, these patterns of thought; see A Closer Look: Logic: A Human Invention?) Think of how popular culture and media often depict characters endowed with logical reasoning. In American slang they are the eggheads, the geeks, the nerds, the ones who can use their minds but have trouble relating to other people. Such people often lack compassion or social charisma, or they are emotionally unex- pressive. They are only logical and lack the blend of attributes that people actually have.

Consider the logically endowed characters on the Star Trek series. Vulcans, for example, are beings who suppress all emotions in favor of logic because they believe that emotions are dangerous. What appear to be heartless decisions by the Vulcans no doubt make logic seem quite unsavory to some viewers. The android Data—from The Next Generation series in the Star Trek franchise—is another example. Data’s positronic brain is devoid of any emotional capacity and thus processes all information exclusively by means of a logical calculus. Logic is thus presented as a source of alienation, as Data yearns for the affective depth that his human colleagues experience, such as humor and love.

Such presentations of logic as the polar opposite of emotion are false dichotomies because all human beings are naturally endowed with both logical and emotional faculties—not just one or the other. In other words, we have a broader range of abilities than that for which we give

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Section 1.2 Three Misconceptions About Logic

ourselves credit. So if you think that you are mostly emotional, then you simply have yet to discover your logical side.

Nonetheless, some believe emotions are the fundamental mark of human beings. It is quite likely that emotion has played a significant role in our survival as a species. Neuroscientists, for example, have discovered that our emotions have a faster pathway to the action centers of the brain than the methodical decision-making approach of our logical faculties (LeDoux, 1986, 1992). It pays, for example, to give no thought to running if we fear we are being hunted by a predator.

In most human civilizations today, however, dodging predators is not a main necessity. In fact, methodical reasoning is more advantageous in most of today’s situations. Thinking things through logically assists learning at all levels, produces better results in the job market (in seeking jobs, obtaining promotions, and procuring raises), and helps us make better choices. As noted in the previous section, we are more likely to be satisfied and experience fewer regrets if we reason carefully about our most critical choices in life. Indeed, logical reasoning can prove to be a better strategy for attaining the individual quest for personal fulfillment than any available alternative such as random choice, emotional impulse, waiting and seeing, and so on.

Moral of the Story: Emotions Versus Logic Embracing logical reasoning does not mean disregarding our emotions altogether. Instead, we should recognize that emotions and logic are both essential components of what it is to be human.

A Closer Look: Logic: A Human Invention? One objection to the use of logic—often from what is known as a postmodern perspective—is that logic is a human invention and thus inferior to emotions or intuitions. In other words, what some call the “rules of logic” cannot be seen as univer- sally applicable because logic originated in the Western world; thus, logic is relative and only a matter of perspective.

For example, the invention of chairs seems indispensable to those of us who live where chairs have become part of our cultural background. But those from different cultural back- grounds or those who lived during different time periods may not use chairs at all, or may employ alternative seating devices, such as the traditional Japanese tatami mats. To broadly apply the concept of chair as an appropriate place to sit would be ethnocentric, or applying the standards of one’s own culture to all other cultures.

In response to the foregoing objection, the authors of this text argue that logic is not a human invention, nor a conven- tion that spread in certain parts of the world. Rather, logic was

Fine Art Images/SuperStock

Aristotle’s Organon is a compilation of six treatises in which Aristotle formulated principles that laid the foundation for the field of logic.


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Section 1.2 Three Misconceptions About Logic

discovered in people’s ordinary encounters with reality, as early as antiquity. Based on avail- able historical records, the first study of the principles at work in good reasoning emerged in ancient Greece. Aristotle was the first to formulate principles of logic, and he did so in six treatises that ancient commentators grouped together under the title Organon, which means “instrument” (reflecting the view that logic is the fundamental instrument for philosophy, which will be discussed later in the chapter).

Importantly, other civilizations have developed logic independently of the Greek tradition. For example, Dignaga was an important thinker in India who lived a few hundred years after Aristotle. Dignaga’s work begins with certain practices of debate within the Nyaya school of Hinduism and transitions to a more formal approach to reasoning. Although the result of Dig- naga’s studies is not identical to Aristotle’s, there is enough similarity to strongly suggest that basic logical principles are not merely cultural artifacts.

In the Middle Ages, Aristotelian logic was brought to the West by Islamic philosophers and thus became part of the scholarship of Christian philosophers until the 14th or 15th century. The emergence of modern logic did not take place until the 19th and 20th centuries, during which new ways of analyzing propositions gave rise to new discoveries concerning the foun- dations of mathematics, as well as a new system of logical notation and a new system of logical principles that replaced the Aristotelian system.

Thus, the examination of good reasoning was fundamental in the development of human civi- lization. Logical reasoning has helped us to identify the laws that guide physical phenomena, which brought us to the state of technological advancement that we experience today. How else could we have erected pyramids and other marvels in the ancient world without having discovered a principle for checking the accuracy of the geometry employed to design them?

Logic Does Not Need to Be Learned A second misconception is that logic does not need to be learned. After all, humankind’s unique distinction among other animals is the faculty of rationality and abstract thought. Although many nonhuman animals have very high levels of intelligence, to the best of our knowledge, abstract thought seems to be the mark of humankind’s particular brand of rationality. Today the applications of logical reasoning are all around us. We are able to experience air travel and marvel at rockets in space. We are also able to enjoy cars, sky- scrapers, computers, cell phones, air-conditioning, home insulation, and even smart homes that allow users to regulate light, temperature, and other functions remotely via smart- phones and other devices. Logical reasoning has afforded us an increasingly better picture of reality, and as a result, our lives have become more comfortable.

However, if logical reasoning is a natural human trait, then why should anyone have to learn it? We certainly experience emotions without any need to be trained, so why would the case be different with our rational capacities? Consider the difference between natural capacities that are nonvoluntary or automatic, on the one hand, and natural capacities that involve our will, on the other. Swallowing, digesting, and breathing are nonvoluntary natural capacities, as are emotions. We usually do not will ourselves to feel happy, angry, or excited. Rather, we usually just find ourselves feeling happy, angry, or excited.

A Closer Look: Logic: A Human Invention? (continued)

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Section 1.2 Three Misconceptions About Logic

Now contrast these with voluntary natural capacities such as walking, running, or sitting. We usually need to will these actions in order for them to take place. We do not just find ourselves running without intending to run, as is the case with swallowing, breathing, or feeling excited or angry. If logic were akin to breathing, the world would likely look like a different place.

Logic is practiced with intention and must be learned, just like we learn to walk, sit, and run. True, almost everyone learns to run to some degree as part of the normal process of growing up. Similarly, almost everyone learns a certain amount of logical reasoning as they move from infant to adult. However, to be a good runner, you need to learn and practice specific skills. Similarly, although everyone has some ability in logic, becoming a good critical thinker requires learning and practicing a range of logical skills.

Logic Is Too Hard The final misconception is that logic is too hard or difficult to learn. If you have survived all these years without studying logic, you might wonder why you should learn it now. It is true that learning logic can be challenging and that it takes time and effort before it feels like second nature. But consider that we face the same challenge whenever we learn anything new, whether it is baking, automotive repair, or astrophysics. These are all areas of human knowledge that have a specific terminology and methodology, and you cannot expect to know how to bake a soufflé, fix a valve cap leak, or explain black holes without any investment in learning the subject matter.

Let us return to our running analogy. Just as we must intend to run in order to do it, we must intend to think methodically in order to do it. When we become adept at running, we do not have to put in as much effort or thought. A fit body can perform physical tasks more easily than an unfit one. The mind is no different. A mind accustomed to logical reasoning will find activities of the intellect easier than an unfit one. The best part is that if you wish to achieve logical fitness, all you need to do is learn and practice the necessary tools for it. The purpose of this book is to guide you toward this goal.

Without a doubt, learning logic will be challenging. But keep in mind that starting a logical fitness program is very much like starting a physical fitness program: There will be a little pain in the beginning. When out-of-shape muscles are exercised, they hurt. You might find that some lessons or concepts might give you a bit of trouble. When this happens, don’t give up! In a physical fitness program, we know that if we keep going, over time the pain goes

Moral of the Story: Logic as a Skill Having a natural capacity for something does not amount to being good at it. Even as emotions seem to come so naturally, some people have to work at being less sensitive or more empa- thetic. The same is true for logical reasoning.

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Section 1.3 What Is Logic?

away, the muscles get in shape, and movement becomes joyful. Likewise, as you keep working diligently on learning and developing your natural logical abilities, you will discover that you understand new things more easily, reading is less of a struggle for you, and logical reasoning is actually fun and rewarding. Eventually, you will begin to recognize logical connections (or the lack thereof) that you did not previously notice, make decisions that you are less likely to regret, and develop the confidence to defend the positions you hold in a way that is less emotionally taxing.

1.3 What Is Logic? Having dispelled some common misconceptions, we can now occupy ourselves with a funda- mental question for this book: What is logic? A first attempt to define logic might be to say that it is the study of the methods and principles of good reasoning. This definition implies that there are certain principles at work in good reasoning and that certain methods have been developed to encourage it. It is important to clarify that these principles and methods are not a matter of opinion. They apply to someone in your hometown as much as to someone in the smallest village on the other side of the world. Furthermore, they are as suitable today as they were 200 or 2,000 years ago.

This definition is a good place to start, but it leaves open the questions of what we mean by “good reasoning” and what makes some reasoning good relative to others. Although it is admittedly difficult to cram answers to all possible questions into a pithy statement, defini- tions should attempt to be more specific. In this book, we shall employ the following defini- tion: Logic is the study of arguments that serve as tools for arriving at warranted judgments. Notice that this definition states how logic can be of service to you now, in your daily routine, and in whatever occupation you hold. To understand how this is the case, let us unpack this definition a bit.

The Study of Arguments This definition of logic does not explain that there are principles at work in good reasoning or that these princi- ples are not necessarily informed by experience: The meaning of the word argument in logic does the job. Argu- ment has a very technical meaning in logic, and for this reason, Chapter 2 is dedicated entirely to the definition of arguments—what they are, what they are not, what they consist of, and what makes them good. Later in this chap- ter, we will survey other meanings for the word argument outside of logic. Purestock/Thinkstock

In logic, an argument is the methodical presentation of one’s position on a topic, not a heated fight with another person.

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Section 1.3 What Is Logic?

For now, let us refer to an argument as a methodical defense of a position. Suppose that Diana is against a proposed increase in the tax rate. She decides to write a letter to the editor to pres- ent her reasons why a tax increase would be detrimental to all. She researches the subject, including what economists have to say about tax increases and the position of the opposition. She then writes an informed defense of her position. By advancing a methodical defense of a position, Diana has prepared an argument.

A Tool for Arriving at Warranted Judgments For our purposes, the word judgment refers simply to an informed evaluation. You examine the evidence with the goal of verifying that if it is not factual, it is at least probable or theo- retically conceivable. When you make a judgment, you are determining whether you think something is true or false, good or bad, right or wrong, beautiful or ugly, real or fake, delicious or disgusting, fun or boring, and so on. It is by means of judgments that we furnish our world of beliefs. The richer our world of beliefs, the clearer we can be about what makes us happy. Judgments are thus very important, so we need to make sure they are sound.

What about the word warrant? Why are warranted judgments preferable to unwarranted ones? What is a warrant? If you are familiar with the criminal justice system or television crime dramas, you may know that a warrant is an authoritative document that permits the search and seizure of potential evidence or the arrest of a person believed to have commit- ted a crime. Without a warrant, such search and seizure, as well as coercing an individual to submit to interrogation or imprisonment, is a violation of the protections and rights that individuals in free societies enjoy. The warrant certifies that the search or arrest of a person is justified—that there is sufficient reason or evidence to show that the search or arrest does not unduly violate the person’s rights. More generally, we say that an action is warranted if it is based on adequate reason or evidence.

Accordingly, our judgments are warranted when there is adequate reason or evidence for making them. In contrast, when we speak of something being unwarranted, we mean that it lacks adequate reason or evidence. For example, unwarranted fears are fears we have without good reason. Children may have unwarranted fears of monsters under their beds. They are afraid of the monsters, but they do not have any real evidence that the monsters are there. Our judgments are unwarranted when, like a child’s belief in lurking monsters under the bed, there is little evidence that they are actually true.

In the criminal justice system, the move from suspicion to arrest must be warranted. Simi- larly, in logic, the move from grounds to judgment must be warranted (see A Closer Look: War- rants for the Belief in God for an example). We want our judgments to be more like a properly executed search warrant than a child’s fear of monsters. If we fail to consider the grounds for our judgments, then we are risking our lives by means of blind decisions; our judgments are no more likely to give us true beliefs than false ones. It is thus essential to master the tools for arriving at warranted judgments.

It is important to recognize the urgency for obtaining such mastery. It is not merely another nice thing to add to the bucket list—something we will get around to doing, right after we trek to the Himalayas. Rather, mastering the argument—the fundamental tool for arriving at

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Section 1.3 What Is Logic?

A Closer Look: Warrants for the Belief in God Striving for warranted judgments might seem difficult when it comes to beliefs that we have accepted on faith. Note that not all that we accept on faith is necessarily related to God or religion. For example, we likely have faith that the sun will rise tomorrow, that our spouses are honest with us, and that the car we parked at the mall will still be there when we return from shopping. Many American children have faith that the tooth fairy will exchange money for baby teeth and that Santa Claus will bring toys come Christmas. Are we reasoning correctly by judging such beliefs as warranted? Whatever your answer in regard to these other issues, questions of religious belief are more likely to be held up as beyond the reach of logic. It is important to recognize this idea is far from being obviously true. Many deeply religious people have nonetheless found it advisable to offer arguments in support of their beliefs.

One such individual was Thomas Aquinas, a 13th-century Roman Catholic Dominican priest and philosopher. In his Summa Theo- logica (Aquinas, 1947), he advanced five logical arguments for God’s existence that do not depend on faith.

The 20th-century Oxford scholar and Christian apologist C. S. Lewis, perhaps best known for the popular children’s series The Chronicles of Narnia, did not embrace his Anglican religion until he was in his thirties. In his books Mere Christianity and Miracles: A Preliminary Study, he employs reason to defend Christian beliefs and the logical possibility of miracles.

There are, of course, many more examples. The important point to draw from this is that all of our judgments of faith—from the faith in the sun rising tomorrow to the faith in the exis- tence of God—should be warranted beliefs and not just beliefs that we readily accept without question. In other words, even faith should make sense in order to be able to communicate such beliefs to those who do not share those beliefs. Note that philosophers who have pre- sented arguments in defense of their religious views have helped transform the nature of reli- gious disagreement to one in which the differences are generally debated in an intellectually enlightening way.

We have not yet reached the point in which differences in religious views are no longer the cause of wars or killing. Nonetheless, the power of argument in the formation of our beliefs is that it supports social harmony despite diversity and disagreement in views, and we all gain from presenting our unique positions in debated issues.


In his Summa Theologica, Thomas Aquinas advanced the idea that belief in the existence of God can be grounded in logical argument.

warranted judgments—is as essential as learning to read and write. Knowledge of logic is a relatively tiny morsel of information compared to all that you know thus far, but it has the capacity to change your life for the better.

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Section 1.4 Arguments Outside of Logic

Formal Versus Informal Logic Logic is a rich and complex field. Our focus here will be how logic contributes to the develop- ment and honing of critical thinking in everyday life. Primarily, the concepts we will discuss will reflect principles of informal logic. The principal aim in informal logic is to examine the reasoning we employ in the ordinary and everyday claims we make.

In contrast, formal logic is far more abstract, often involving the use of symbols and math- ematics to analyze arguments. Although this text will touch on a few formal concepts of logic in its discussions of deduction (see Chapter 3 and Chapter 4), the purpose in doing so is to develop methodology for good reasoning that is directly applicable to ordinary life.

1.4 Arguments Outside of Logic Although Chapter 2 will explore the term argument in more detail, it is important to clarify that the word is not exclusive to logic. Its meaning varies widely, and you may find that one of the descriptions in this section fits your own understanding of what is an argument. Knowing there is more than one meaning of this word, depending on context or application, will help you correctly understand what is meant in a given situation.

Arguments in Ordinary Language Often, we apply the word argument to an exchange of diverging views, sometimes in a heated, angry, or hostile setting. Suppose you have a friend named Lola, and she tells you, “I had an argument with a colleague at work.” In an ordinary setting you might be correct in under- standing Lola’s meaning of the term argument as equivalent to a verbal dispute. In logic, how- ever, an argument does not refer to a fight or an angry dispute. Moreover, in logic an argument does not involve an exchange between two people, and it does not necessarily have an emo- tional context.

Although in ordinary language an argument requires that at least two or more people be involved in an exchange, this is not the case in logic. A logical argument is typically advanced by only one person, either on his or her behalf or as the representative of a group. No exchange is required. Although an argument may be presented as an objection to another person’s point of view, there need not be an actual exchange of opposing ideas as a result.

Now, if two persons coordinate a presentation of their defenses of what can be identified as opposing points of view, then we have a debate. A debate may contain several arguments but is not itself an argument. Accordingly, only debates are exchanges of diverging views.

Even if a logical argument is both well supported and heartfelt, its emotional context is not its driving force. Rather, any emotion that may be inevitably tied in with the defense of the argu- ment’s principal claim is secondary to the reasons advanced. But let us add a little contextual reference to the matter of debates. If the arguments on each side of the debate are presented

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Section 1.4 Arguments Outside of Logic

well, then the debate may lead to the discovery of perspectives that each party had not pre- viously considered. As such, debates can be quite enlightening because every time our own perspective is broadened with ideas not previously considered and that are well supported and defended, it is very difficult for the experience to be negative. Instead, a good debate is an intellectually exhilarating experience, regardless of how attached one may be to the side one is defending.

Not even debates need to be carried out with an angry or hostile demeanor, or as a means to vent one’s frustration or other emotions toward the opposition. To surrender to one’s emo- tions in the midst of a debate can cause one to lose track of the opposition’s objections and, consequently, be able to muster only weak rebuttals.

Rhetorical Arguments Think about how politicians might try to persuade you to vote for them. They may appeal to your patriotism. They may suggest that if the other candidate wins, things will go badly. They may choose words and examples that help specific audiences feel like the politician empathizes with their situation. All of these techniques can be effective, and all are part of what someone who studies rhetoric—the art of persuasion—might include under the term argument.

Rhetoric is a field that uses the word argument almost as much as logic does. You are likely to encounter this use in English, communication, composition, or argumentation classes. From the point of view of rhetoric, an argument is an attempt to persuade—to change someone’s opinion or behavior. Because the goal of a rhetorical argument is persuasion, good arguments are those that are persuasive. In fact, any time someone attempts to persuade you to do some- thing, they can be seen as advancing an argument in this sense.

Moral of the Story: Defining the Word Argument To avoid conflating the two widely different uses of the word argument (that is, as a dis- pute in ordinary language and as a defense of a point of view in logic) is to use the word only in its classical sense. In its classical meaning, an argument does not refer to a vehicle to express emotions, complaints, insults, or provocations. For these and all other related meanings, there are a wide variety of terms that would do a better job, such as disagree- ment, quarrel, bicker, squabble, fight, brawl, altercation, having words, insult match, word combat, and so on. The more precise we are in our selection of words, the more efficient our communications.

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Section 1.4 Arguments Outside of Logic

Think about how you might have persuaded a sibling to do something for you when you were young. You might have offered money, tried to manipulate with guilt-inducing tactics, appealed to his or her sense of pride or duty, or just attempted to reason with him or her. All of these things can be motivating, and all may be part of a rhetorical approach to argu- ments. However, while getting someone to do something out of greed, guilt, pride, or pity can indeed get you what you want, this does not mean you have succeeded in achieving a justified defense of your position.

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