# Talk:Proof by Contradiction/Also known as

If there are cases where RaA is invoked when PbC is meant, and the other way around, we need to change the pages as necessary. If you really, really, really think it's more worthwhile than adding new stuff. --prime mover (talk) 03:54, 12 October 2018 (EDT)

- I know. This would be a lot of work and really only of interested to intuitionistic mathematicians. I guess I will wait until one of them comes along. Until then, I will cheerfully call both RaA and PbC proofs by contradiction, as they are really the same thing in mainstream logic/maths.

- I am sure that there must be many such cases though, as ProofWiki does not even have a proof type category for Reductio ad Absurdum (as is understandable). KarlFrei (talk) 04:02, 12 October 2018 (EDT)

- ...so I don't quite understand why you reverted my edit, as I only just noticed. KarlFrei (talk) 04:03, 12 October 2018 (EDT)

- Because it is not the intention to leave $\mathsf{Pr} \infty \mathsf{fWiki}$ in such a substandard state as to not make that distinction. Yes, a lot of work will need to be done to amend it. I'm on the case. --prime mover (talk) 04:29, 12 October 2018 (EDT)

It seems there is lots of confusion on this topic. (I guess I am glad that it is not just me.) Wikipedia claims that proof by contradiction is a special case of reductio ad absurdum. [1] It also has a long discussion on this topic [2]. Meanwhile, another author [3] says

- Proof of negation is the one that starts with a positive assumption (what we call proof by contradiction)
- Proof by contradiction starts with a negative assumption (our reductio ad absurdum)...

It seems to be a real mess.

- Perhaps we ought to abandon the entire enterprise. --prime mover (talk) 05:24, 12 October 2018 (EDT)