The word fallacy is often used to describe a popular mistaken belief. “Fat is bad” might be said to be a fallacy, since many people do not know that some fats are good for health. However, such factual mistakes are not regarded as fallacies in critical thinking. In this book, a fallacy is a mistake that violates the principles of correct reasoning. Under this definition, a person can commit a fallacy without making any factual error. Suppose someone argues as follows:
This is not a good argument because the conclusion does not follow from the premises. It is quite possible that those cats with short tails are different from those with black hair. Of course, as a matter of fact, some cats have both short tails and black hair. So the premises and the conclusion are all true. But this is still a bad argument. Someone who accepts this argument would indeed be committing a fallacy, but it involves no mistake about empirical facts.
One further clarification: Many critical thinking textbooks define a fallacy as a bad or unreliable argument. But many commonly recognized fallacies do not take the Form of an argument. For example, a contradictory claim is often regarded as fallacious, but a single claim is not an argument. Similarly, as we shall see, a question with an inappropriate assumption can also be a fallacy, but a question is not an argument. But both cases ...