An analogy features the similarities between two different things. A faulty comparison or analogy can deceive by asserting similarity between two things that are fundamentally dissimilar (e.g., analogizing the threat posed by the Patient Protection and Affordable Care Act to the threat posed by Nazi Germany or likening an elected U.S. leader to Hitler because one disagrees with his policies or actions). Alternatively a faulty analogy may invite the unjustified inference that because two things are similar in some ways, they must be in others. Since false analogy gains power by attaching the feelings we have toward one object to another object, one might consider it a form of Guilt by Association.

We can test an analogy by asking whether the supposed similarity actually exists, whether it is relevant to the argument being advanced, and whether relevant similarities between the compared objects outweigh the relevant differences.