5.5 Informal Fallacies

By the end of this section, you will be able to:

• Explain the four general categories of informal fallacies.
• Classify fallacies by general category.
• Identify fallacies in ordinary language.

Reasoning can go wrong in many ways. When the form of an argument is problematic, it is called a formalfallacy. Mistakes in reasoning are not usually caused by the structure of the argument. Rather, there is usually a problem in the relationship between the evidence given in the premises and the conclusion. Take the following example:

I don’t think Ms. Timmons will make a good mayor. I’ve got a bad feeling about her. And I’ve heard she’s not a Christian. Furthermore, the last time we had a female mayor, the city nearly went bankrupt. Don’t vote for Ms. Timmons.

Notice that to assess the above argument, you have must think about whether the reasons offered function as evidence for the conclusion that Ms. Timmons would be a bad mayor. This assessment requires background knowledge about the world. Does belonging to a specific religion have any bearing on one’s qualification for mayor? Is there any credible connection between a mayor’s gender and the likelihood that person will cause a bankruptcy? If the reasons are not adequate support for the conclusion, then the reasoner commits an informal fallacy. In the above argument, none of the reasons offered support for the conclusion. In fact, each reason commits a different fallacy. The first reason is based on an appeal to emotion, which is not relevant. The second reason points to a characteristic (religion) that is irrelevant in judging competency, and the third reason creates a spurious connection between the candidate and a previous female mayor, putting them both in the same failed category based solely on the fact that they share the same gender.

There are many specific types of informal fallacies, but most can be sorted into four general categories according to how the reasoning fails. These categories show how reasoning can go wrong and serve as warnings for what to watch out for in arguments. They are (1) fallacies of relevance, (2) fallacies of weak induction, (3) fallacies of unwarranted assumption, and (4) fallacies of diversion.