- the reasoning that, when a conditional statement is accepted as true, as “If X is red, then Y is blue,” it can be inferred when the antecedent is known to be true, as “X is red,” that its consequent, “Y is blue,” is affirmed.
- an argument based on the reasoning of modus ponens: A simple modus ponens might begin with “If Joe sneezes, Tom laughs.”
- the principle that whenever a conditional statement and its antecedent are given to be true its consequent may be validly inferred, as in if it's Tuesday this must be Belgium and it's Tuesday so this must be Belgium
