What Is a Fallacy?

Suppose I ask you to multiply two large numbers-say 12,653 and 65,321. How would you get the correct answer? You’d probably use a calculator or the good old multiplication algorithm you learned as a kid. One thing is clear: if you don’t use the correct method, then you’re not guaranteed to get the correct answer.

Suppose now that I ask you to defend some claim that you believe-that I ask you to give me reasons, in other words, to believe that the claim is true. What’s true in the multiplication case is also true here: if your reasoning doesn’t follow a correct method, then you’re not guaranteed to get a correct conclusion.

Reasoning, or argumentation, is the process of supporting a statement by appeal to other statements. The statement you’re trying to support is called the conclusion, and the statements that are supposed to support it are called premises. Reasoning can be correct or incorrect in just the way that mathematical calculation can. When reasoning is performed incorrectly, we say that it commits a fallacy.

A fallacy is an error in reasoning.

The telltale sign of a fallacy is this: even if your premises are true, they still tell you nothing about whether or not your conclusion is true. Let’s look at an example. Here are two arguments: