Introduction to Logic and Critical Thinking

This is an introductory textbook in logic and critical thinking. The goal of the textbook is to provide the reader with a set of tools and skills that will enable them to identify and evaluate arguments. The book is intended for an introductory course that covers both formal and informal logic. As such, it is not a formal logic textbook, but is closer to what one would find marketed as a “critical thinking textbook.” The formal logic in chapter 2 is intended to give an elementary introduction to formal logic. Specifically, chapter 2 introduces several different formal methods for determining whether an argument is valid or invalid (truth tables, proofs, Venn diagrams). I contrast these formal methods with the informal method of determining validity introduced in chapter 1. What I take to be the central theoretical lesson with respect to the formal logic is simply that of understanding the difference between formal and informal methods of evaluating an argument’s validity. I believe there are also practical benefits of learning the formal logic. First and foremost, once one has internalized some of the valid forms of argument, it is easy to impose these structures on arguments one encounters. The ability to do this can be of use in evaluating an argumentative passage, especially when the argument concerns a topic with which one is not very familiar (such as on the GRE or LSAT).
However, what I take to be of far more practical importance is the skill of being able to reconstruct and evaluate arguments. This skill is addressed in chapter 1, where the central ideas are that of using the principle of charity to put arguments into standard form and of using the informal test of validity to evaluate those arguments. Since the ability to reconstruct and evaluate arguments is a skill, one must practice in order to acquire it. The exercises in each section are intended to give students some practice, but in order to really master the skill, one must practice much, much more than simply completing the exercises in the text. It makes about as much sense to say that one could become a critical thinker by reading a critical thinking textbook as that one could become fluent in French by reading a French textbook. Logic and critical thinking, like learning a foreign language, takes practice because it is a skill.

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