A → B
– (if A, then B) Premise 2:
C → D
– (if C, then D) Premise 3:
A ∨ C
– (A or C) Conclusion:
B ∨ D
– (B or D)
The constructive dilemma can be seen as a combination of two Modus Ponens which are connected by a disjunct statement.
The term “dilemma” in this context should be understood as a “decision” between two conditionals.
An example for a constructive dilemma could be:
If the sun shines tomorrow, [then] we will go to the beach.
If it rains tomorrow, [then] we will go to the museum.
Tomorrow the sun will shine, or it will rain [or both].
Therefore we will tomorrow go to the museum or to the beach [or both].
- Constructive dilemma on Wikipedia