One characteristic of evidence we have just discussed is relevance. Fallacies that result from using evidence that’s irrelevant to the claim fall under the general heading of red herrings. (The term derives from the dried fish that trainers used to distract dogs when teaching them to hunt foxes.) A red herring occurs when a speaker skips to a new and irrelevant topic in order to avoid the topic of discussion. If Politician X says, “We can debate these regulations until the cows come home, but what the American people want to know is, when are we going to end this partisan bickering?” she has effectively avoided providing evidence on the benefits or detriments of the regulations by trying to change the subject to that of partisanship.

One common type of red herring is an ad hominem fallacy. Ad hominem is Latin for “against the man”; the phrase refers to the diversionary tactic of switching the argument from the issue at hand to the character of the other speaker. If you argue that a park in your community should not be renovated because the person supporting it was arrested during a domestic dispute, then you are guilty of ad hominem—arguing against the person rather than addressing the issue. This fallacy is frequently misunderstood to mean that any instance of questioning someone’s character is ad hominem. Not so. It is absolutely valid to call a person’s character into question if it is relevant to the topic at hand. For example, if a court case hinges on the testimony of a single witness and that person happens to be a con artist, then his character is absolutely relevant in deciding whether he is a credible witness.

Analogy is the most vulnerable type of evidence because it is always susceptible to the charge that two things are not comparable, resulting in a faulty analogy. However, some analogies are more vulnerable than others, particularly those that focus on irrelevant or inconsequential similarities between two things. Whenever analogy is used, it’s important to gauge whether the dissimilarities outweigh the similarities. Advertisements sometimes draw faulty analogies to appeal to pathos; for example, an ad for a very expensive watch might picture a well-known athlete or a ballet dancer and draw an analogy between the precision and artistry of (1) the person and (2) the mechanism. When writers use analogy to add drama to a claim, it’s important to question whether the similarities really fit and illuminate the point or simply add emotional appeal. For instance, to argue that “we put animals who are in irreversible pain out of their misery, so we should do the same for people” asks the reader to ignore significant and profound differences between animals and people. The analogy may at first glance appeal to emotions, but it is logically irrelevant.