# 21 Mar modus tollens

Another inference rule used to prove correctness or truth value of logical propositions. The form of the rule is this: If we know that when A is true, B is also true, and we know that A is not true, then we can infer that B is not true. In shorthand the conditions can be expressed A => B AND NOT A. In more terse language we might say premise 1 is IF A THEN B, premise 2 is NOT A, and the conclusion is, therefore NOT B.

**Keywords**: modus ponens

logic

inference

causal relations

dichotomous logic

determinism

logical form

**References**: comprehension

formalisms

information/entropy

logic

rules