對於我們解決的任何爭論,例如以下 通過“通過矛盾證明”方法:
- (A v B)
- (A ⊃ C)
- (B ⊃ D)
[ Therefore, (C v D) - Assumption: ~(C v D)
- Therefore, ~C {from 4}
- Therefore, ~D {from 4}
- Therefore, ~A {from 2 and 5; Modus-tollens}
- Therefore, B {from 1 and 7; by Disjunctive syllogism}
- Therefore, ~B {from 3 and 6; Modus-tollens}
- Therefore, (C v D) {from 4; 8 contradicts 9 our argument is valid}
如果我們得到一個矛盾,比如我帶著8和9來到這裏,我們如何確定這使得論證有效?我們不需要檢查A,C和D是否也相互矛盾?