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Deciding What to Do and Believe

Second Edition


Department of Philosophy
Ryerson University
Toronto, ON, Canada

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For Jane,
my beloved and my friend.


In preparing this Second Edition, I have benefited from many people's advice. First, I would like to thank all of the students at Ryerson University who have taken my critical thinking courses, and all of the graduate students who have worked for me as a TA. I have learned a lot from you all about how to organize, simplify, and present this material. I have also benefited from detailed and constructive comments on every chapter from my colleague, Klaas Kraay.


This book has been a long time in the making, and has benefited from the influence of a huge number of colleagues, friends, and family. Here is an inevitably incomplete accounting of some of these debts.

I first began to think systematically about the nature, value, and pedagogy of critical thinking as an assistant professor of philosophy at Buffalo State College and it would be difficult to overstate the influence of my colleague George Hole on my thinking. He is one of the most gifted philosophy teachers I have ever known and I learned a good deal from him on how to teach philosophy. But even more than this, I am indebted to him for the way he so easily mixes philosophy, wit, and good humor in equal parts. I learned more from him than from anyone about how to teach critical thinking, and about the central role it ought to play in education and in a full life. I also owe a great deal to Gerry Nosich, whose work on critical thinking is without equal. Gerry joined us at Buffalo State College as we were designing and implementing a required first-year critical thinking course, and his gentle and wise advice proved invaluable. While with SUNY, I worked on a statewide committee to design a rubric for the assessment of critical thinking. I learned a lot in this time about the importance of teaching critical thinking across the curriculum, and I am especially indebted to Shir Filler.

Since beginning the writing of this book, I have learned a good deal from my new colleagues at Ryerson University, where the philosophy department teaches several sections of a critical thinking course that is required by students in several programs. I owe special debts to Andrew Hunter, Klaas Kraay, David Ciavatta, Jim Dianda, and Paul Raymont.

I am indebted to Steve Quigley, my editor at Wiley, for gently persuading me to write the book; to Jackie Palmieri, an editorial assistant at Wiley, for gently persuading me to complete it on time; and to several anonymous referees who provided useful feedback on my initial proposal.

I am enormously indebted to my family. I learned as much about how to think critically from my parents as from anyone. They showed me that critical thinking begins at home, and that is a lesson that Miranda and Emily, my wonderful daughters, now champion with exhausting ingenuity.

My greatest and deepest debts, however, are to Jane, whose love and support have never been conditional on sufficient and acceptable reasons or on anything else.


Teaching students to think critically is more about imparting a set of skills and habits than about teaching bits of theory. In developing this textbook, I tried to incorporate several features that I thought would make teaching critical thinking both easier and more effective.

Most significantly, I steered clear of any formal notation aside from the very simplest. It is not that I doubt the value of learning formal logic. In fact, I think that many students thrive while studying it. But in my experience there is so much that most students need to learn before they can see the value of mastering a formal system, and so much more benefit they can derive from a non-formal approach to critical thinking. Instead, I tried to think of this text as like an introduction to practical or applied epistemology: offering systematic advice, and lots of practice, on the best way to go about deciding what to believe and what to do.

It is worth noting here that I treat what is sometimes called enumerative induction as a form of reasoning by analogy. It seems to me that using samples to draw a conclusion about an entire group or population just is reasoning by analogy, and that it can be usefully taught as such. I also say, and this perhaps is more controversial, that reasoning by analogy can be valid. Of course, I do not mean that it is formally valid in the way that modus ponens is formally valid. Reasoning is valid when it is not possible for the premises to be true and the conclusion to be false. The fact that some reasoning can be known to be valid just from its form alone is, of course, important, and I discuss some of these forms in chapters 5 and 6. But it is important to keep in mind that not all valid arguments are formally valid, (e.g., The table is blue, therefore it is colored), and not all arguments that are formally invalid are really invalid (e.g., If Jones is a male, then he is a bachelor; Jones is a bachelor; so, Jones is a male.) Judgment is always needed, it seems to me, in assessing the strength of a piece of reasoning, and this judgment is better taught by focusing on the idea of validity itself. I also think that what I say in Chapter 6 makes a reasonable and pedagogically responsible case for my view that reasoning by analogy can be valid.

I had originally planned to dedicate a chapter to thinking critically about what to do. But I worried that much of it would simply repeat points that had been made earlier and, in so doing, would make deciding what to do seem like a lesser cousin to deciding what to believe. As I worked (and then re-worked) the first 6 chapters, it seemed to me that I could elegantly discuss deciding what to do as we went along, when the topic at hand seemed relevant. I have thus included several “boxes” discussing various aspects of deciding what to do.

The book includes several other kinds of boxes as well. Some identify important mistakes that a good critical thinker ought to avoid. Some provide summaries of the discussion in the body of the text. Some offer examples of critical thinking across the curriculum. Some offer practical tips and rules of thumb. All are intended to make the text more readable and the concepts and skills more accessible.

I also decided that rather than dedicate a chapter to informal fallacies, I would discuss them in what struck me as their proper context. It seems to me that there is no easy way to organize the different kinds of mistakes into a small number of categories without distorting their differences or exaggerating their similarities. Some of the mistakes have to do with clarifying meaning; others with ascribing views to others; some with assessing evidence; others with assessing validity. Several mistakes can occur at several otherwise quite distinct stages in deciding what to do or to believe. Rather than try to force the various mistakes into artificial categories, it seemed to me better to discuss them as we went along. For easy reference, though, I have collected them all in an appendix at the end of the book.

Careful training and repeated practice are crucial to learning any skill, and critical thinking is no exception. I have tried to include a large and varied collection of exercises. But I strongly encourage you to bring your own exercises to class and to encourage your students to seek out arguments and reasoning to share during the class time. In my experience, students learn far more when they are required during class time to participate in the construction, analysis, and assessment of examples of reasoning about what to do or believe. I have included, at the end of most of the chapters, exercises that are specially designed to help students transfer the concepts and skills they are learning to other corners of their lives. My thought is simply that there is little point in teaching someone to think critically if they see no place for it at home, in their own discipline, or at work. Over the years I have experimented with all of these exercises, making adjustments as I went along. The exercises are in a form that I find to be both effective and not overly intrusive. But I encourage you to adjust, alter, add, subtract, and modify as you see fit. The important thing is to find ways to help students see that they are learning skills and concepts that have application and value after the final exam.