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destructive dilemma

Two conditionals plus "one result fails or the other does" give "one condition fails or the other does."

Destructive dilemma is the valid form: if P, then Q; if R, then S; not Q or not S; therefore not P or not R. It works like modus tollens applied to two conditionals at once.

Examples

  • "If the recipe is right, the bread rises. If the oven is hot, the crust browns. The bread didn't rise or the crust didn't brown. So the recipe is wrong or the oven isn't hot."

See also

constructive dilemma modus tollens
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