Consider all. Test All. Hold on to the good.

Illogic Primer Quotes Clippings Books and Bibliography Paper Trails Links Film

Syllogistic Errors

The fallacies in this section are all cases of invalid categorical syllogisms. A categorical syllogism is an argument consisting of exactly three categorical propositions (two premises and a conclusion) in which there appear a total of exactly three categorical terms, each of which is used exactly twice. For example, the classic: (1) All men are mortal. (2) Socrates is a man. Therefore, (3) Socrates is mortal.

Affirming the Consequent


Drawing Affirmative Conclusion


Exclusive Premises

A standard form categorical syllogism has two negative premises (a negative premise is any premise of the form ‘No S are P’ or ‘Some S is not P’).

Existential Fallacy

A particular conclusion is drawn from universal premises.

Four Terms


Illicit Major


Undistributed Middle
