Deductive Fallacy - Logical Fallacy

Logical Fallacy

The standard Aristotelian logical fallacies are:

• Fallacy of four terms (Quaternio terminorum);
• Fallacy of the undistributed middle;
• Fallacy of illicit process of the major or the minor term; and
• Affirmative conclusion from a negative premise.

Other logical fallacies include:

• The self-reliant fallacy

In philosophy, the term logical fallacy properly refers to a formal fallacy—a flaw in the structure of a deductive argument, which renders the argument invalid.

However, it is often used more generally in informal discourse to mean an argument that is problematic for any reason, and thus encompasses informal fallacies as well as formal fallacies—valid but unsound claims or poor non-deductive argumentation.

The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion (see fallacy fallacy). Both may actually be true, or even more probable as a result of the argument (e.g. appeal to authority), but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described. By extension, an argument can contain a formal fallacy even if the argument is not a deductive one; for instance an inductive argument that incorrectly applies principles of probability or causality can be said to commit a formal fallacy.