Illicit process

Describes an (invalid) syllogism, in which either the major or minor term is not used according to the rules of distributivity.

Example of a syllogism Show in Syllogism-Finder App with an undistributed minor term:

All dogs are mamals.
All mamals are animals.
Therefore, all animals are dogs.

All three statements here are of type A (“All S are P”), in which the subject (“S”) is in a distributed and the predicate (“P”) in an undistributed position. For a syllogism to be valid, any term that is in a distributed position in the conclusion would also need to be distributed in the premise. As this is not the case with the minor term (“animals”), this syllogism is formally invalid.

• Undistributed major / minor [term]
• Illicit [process of the] major / minor [term]

The distribution rules for syllogisms are summarized in the article on distributivity. The specific rule that is violated by this fallacy can be formulated as follows:

The following table gives an overview of the distributivity of the terms in the four categorical statement types:

In regard to the example above, the premises therein are all of the type A; While the minor term (“animals”) appears in the conclusion in a distributed position, it is undistributed in the minor statement. Therefore, this form of a syllogism is not valid.

• Distributivity
• Undistributed middle

• Illicit major and Illicit minor on Wikipedia
• Illicit process on RationalWiki
• Illicit Process on Fallacy Files
• Illicit major and Illicit Minor on Logically Fallacious