Originally Posted by

**Lprdgecko** I'm studying for a test and am doing some practice problems. I ran across this one in the Valid Arguments section. (I'll use ~ for the "not" symbol)

Directions: Derive T

(1) P --> Q

(2) ~R --> ~Q

(3) R --> S

(4) P v T

(5) ~S

-----------------------------

(6) ~R ......... (3)(5) Modus Tollens

(7) ~Q ......... (2)(6) Modus Ponens

(8) ~P...........(2)(7) Modus Tollens

(9) ... This is where I'm stuck

I can see that since ~P is true, then P must be false, and thus, to make P v T true, T must be true, but which "property" would I use?

Sorry if this is a re-post. The internet froze up when I clicked the "submit new thread" button last time.