Fallacy

In informal logic and rhetoric, a fallacy is usually an error in reasoning often due to a misconception or a presumption. Some so-called fallacies are not rhetorically intended to appeal to reason but rather to emotion, or a more nuanced disposition. An informal analysis of rhetorical patterns in fallacies should not be confused with rigorously formal arguments in logic, because rationally persuasive arguments require neither to be successful.

Though often used unintentionally, so-called fallacies can be used purposefully to win arguments. Such rhetorical devices, discussed in more detail below, are: "ignoring the question" to divert argument to unrelated issues using a red herring; making the argument personal (argumentum ad hominem) and discrediting the opposition's character, "begging the question" (petitio principi), the use of the non-sequitur, false cause and effect (post hoc ergo propter hoc), bandwagoning (everyone says so), the "false dilemma" or "either-or fallacy" in which the situation is oversimplified, "card-stacking" or selective use of facts, "false equivalence", and "false analogy". Another common device is the "false generalization", an abstraction of the argument that shifts discussion to platitudes where the facts of the matter are lost. There are many more tricks to divert attention from careful exploration of a subject.

A well defined formal fallacy, logical fallacy or deductive fallacy, is typically called an invalid argument. An informal fallacy is argument that may fail to be rationally persuasive.