Constructive dilemma[1][2][3] is a valid rule of inference of propositional logic.

In sum, if two conditionals are true and at least one of their antecedents is, then at least one of their consequents must be too.

Constructive dilemma is the disjunctive version of modus ponens, whereas destructive dilemma is the disjunctive version of modus tollens.

The constructive dilemma rule may be written in sequent notation: where

in some logical system; and expressed as a truth-functional tautology or theorem of propositional logic: where

are propositions expressed in some formal system.

The dilemma derives its name because of the transfer of disjunctive operator.

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