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.