Constructive Dilemma
Constructive dilemma is a deductively valid form combining a disjunction with two conditionals.
P1) P or Q. (P ∨ Q)
P2) If P, then R. (P → R)
P3) If Q, then S. (Q → S)
∴
C) R or S. (R ∨ S)
Whichever side of the disjunction holds, you’re guaranteed one of the two consequents.
Example
1. It will be sunny or it will rain tomorrow. 2. If sunny, we go to the beach. 3. If raining, we go to the theatre. ∴ 4. We go to the beach or the theatre.