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Illicit process

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An illicit process and its two forms, the illicit major and the illicit minor, is a logical fallacy in which a flawed conclusion is reached by improper (illicit) distribution in the conclusion of the terms used in the premises.

The fallacy is a syllogistic fallacy and a formal fallacy.


Distributed means that is appears either as "all X" or as "are not X". This means that you have a strong knowledge about X.

Undistributed means it appears as either "some X" or as "are X". This means that you have a rather weak knowledge about X.

So, being undistributed in the premise means that the premises don't say anything about all X. Thus, the knowledge about all X can't appear suddenly in the conclusion.


An illicit process has two forms.

Illicit major[edit]

P1: All X are Y.
P2: All Z are not X.
C1: All Z are not Y.


P1: All Middle are Major.
P2: All Minor are not Middle.
C1: All Minor are not Major.

Illicit minor[edit]

P1: All X are Y.
P2: All X are Z.
C1: All Y are Z.


P1: All Middle are Major.
P2: All Middle are Minor.
C1: All Major are Minor.


Illicit major[edit]

P1: All dogs are mammals.
P2: No cats are dogs.
C1: Therefore, no cats are mammals.

In this argument, the major term is "mammals". This is distributed in the conclusion (the last statement) because we are making a claim about a property of all mammals: that they are not cats. However, it is not distributed in the major premise (the first statement) where we are only talking about a property of some mammals: Only some mammals are dogs.

Illicit minor[edit]

P1: All cats are felines.
P2: All cats are mammals.
C1: All mammals are felines.

The minor term here is mammal, which is not distributed in the minor premise "All cats are mammals," because this premise is only defining a property of possibly some mammals (i.e., that they're cats.) However, in the conclusion "All mammals are felines," mammal is distributed (it is talking about all mammals being felines). It is shown to be false by any mammal that is not a feline; for example, a dog.


In his critique of a creationist article on genetic recombination, Alec MacAndrew identifies several logical flaws including the illicit process of the following form [1]:

P1: All recombination causes change in DNA sequences.
P2: All recombination is regulated by cellular mechanisms.
C1: Therefore, all changes in DNA sequence are regulated by cellular mechanisms.

The flaw is that, while recombination may cause change in DNA sequences, it is not proposed as causing all change in DNA sequences. However, the conclusion is about all DNA sequences. The major premise does not distribute across all DNA sequences while the conclusion does.

Illicit observation[edit]

See the main article on this topic: illicit observation

An illicit observation is not an error of illicit process but of ambiguity.

See also[edit]

External links[edit]


  1. Alec MacAndrew's Genetic Recombination Misused, a critique of Christopher Ashcroft's A New Look at Genetic Recombination