Handout for Categorical Syllogisms PHIL 121 Methods of Reasoning

Figures: 1st figure 2nd figure 3rd figure 4th figure M – P P – M M – P P – M S – M S – M M – S M – S ∴ S – P ∴ S – P ∴ S – P ∴ S – P

Syllogistic Fallacies 1. Fallacy of four terms . If a categorical syllogism has more than three terms, then it commits the fallacy of four terms. . Note: sometimes a categorical syllogism appears to commit this fallacy, but doesn't, really. If one of the four terms is the complement of another term in the syllogism, it is highly possible that the fourth term can be eliminated by subjecting one or more of the premises to a series of immediate inferences (thus transforming one of the terms into its complement). 2. Fallacy of the undistributed middle . The middle term must be distributed in at least one of the premises in a standard form categorical syllogism; otherwise the syllogism commits the fallacy of the undistributed middle. 3. Fallacy of illicit major . If the major term is distributed in the conclusion, then it must also be distributed in the major premise; otherwise the syllogism commits the fallacy of illicit major. 4. Fallacy of illicit minor . If the minor term is distributed in the conclusion, then it must also be distributed in the minor premise; otherwise the syllogism commits the fallacy of illicit minor. 5. Fallacy of exclusive premises . Any standard form categorical syllogism with two negative premises commits the fallacy of exclusive premises. 6. Fallacy of drawing an affirmative conclusion from a negative premise(s) . Any standard form categorical syllogism with a negative premise must also have a negative conclusion; otherwise it commits the fallacy of drawing an affirmative conclusion from a negative premise(s). 7. Existential fallacy . Any standard form categorical syllogism with two universal premises and a particular conclusion commits the existential fallacy.

Karin Howe Binghamton University Spring 2013