3 - Basic Valid and Invalid Forms

pure skeletons. No animals. No stories. Just pattern shapes.

Modus Ponens

If A then B A Therefore B

Modus Tollens

If A then B Not B Therefore Not A

Hypothetical Syllogism

If A then B If B then C Therefore If A then C

Disjunctive Syllogism

A or B Not A Therefore B

Simple Dilemma

A or B If A then C If B then C Therefore C

Complex Dilemma

A or B If A then C If B then D Therefore C or D

Fallacy Affirming the Consequent

If A then B B Therefore A

Fallacy Denying the Antecedent

If A then B Not A Therefore Not B