Formal fallacies

In philosophy, a formal fallacy, deductive fallacy, logical fallacy or non sequitur (Latin for “it does not follow”) is a pattern of reasoning rendered invalid by a flaw in its logical structure that can neatly be expressed in a standard logic system, for example propositional logic. It is defined as a deductive argument that is invalid. The argument itself could have true premises, but still have a false conclusion. Thus, a formal fallacy is a fallacy where deduction goes wrong, and is no longer a logical process. This may not affect the truth of the conclusion, since validity and truth are separate in formal logic. [1]

Informal fallacies

In contrast to a formal fallacy, an informal fallacy originates in a reasoning error other than a flaw in the logical form of the argument. A deductive argument containing an informal fallacy may be formally valid, but still remain rationally unpersuasive. Nevertheless, informal fallacies apply to both deductive and non-deductive arguments. [2]

Examples of informal fallacies[3]


  1. Wikipedia: Formal Fallacies ↩︎

  2. Wikipedia: Informal Fallacies ↩︎

  3. Douglas Walton: Why Fallacies Appear to Be Better Arguments than They Are (2010, accessed 2020-06-04) ↩︎