Could Reductio ad Absurdum not be consireded a valid proof method? Are there any compelling arguments against it, or at it's favor?
I feel like I am assuming some metamathematical hypothesis about my set of axioms that may not be true, when I use it. So I always try to convert it to a Contrapositive. But I don't know of any arguments or even bibliography about this matter.
Edit: As some have pointed, this question is somewhat related to (http://mathoverflow.net/questions/12342/reductio-ad-absurdum-or-the-contrapositive). However, I want to understand what are metamathematically the justifications for the method of Reductio and if there are arguments against it.