Phil 155 Final Exam

Front 1

Disjunction Elimination

Back 1

Also called proof by cases.
1. P v Q
2. | | | >>P
3. | | | >> . . .
4. | | | >>-------
5. | | | >>S

>>Q
>> . . .
>>-------
>>S
S

{Given P or Q, create two separate subproofs, under which you prove that S follows not only from P alone, but that S also follows from Q alone. Conclude that S follows in general [back in the main proof]}

Front 2

Negation Introduction

Back 2

1. >>P
2. >> . .. .
3. >> ⊥
4. ~P

{Assuming temporarily P. If, in that subproof, you can prove that an absurdity necessarily follows from assuming P, then you can conclude, outside of that subproof, NOT - P [~P]}