## What were Descartes's justifications for the human ability to doubt, and why did he think it was so important?

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In his Meditations on First Philosophy, Rene Descartes resolved to systematically doubt that any of his beliefs were true. This was done in order to build a system of belief that would consist of only true beliefs.

It appears that the ability to doubt is the core foundation of Descartes's philosophy. But did Descartes ever justify specifically why one even has the ability to doubt? If so, what were his principal arguments?

I would think it likely that he did indeed make such assertions, however I am having a difficult time finding a source. – E1Suave – 2012-05-04T03:42:24.393

2Your second round of edits made this question much better. I made a minor tweak to the title so that it actually asks a question and doesn't have a tag like (Descartes) thrown in at the end. Hopefully I didn't misrepresent your question! – Cody Gray – 2012-05-04T07:02:47.863

@CodyGray I have no problem with your edit and appreciate your help. Hopefully, as I gain experience utilizing this site my questions will become more succinct. – E1Suave – 2012-05-04T12:08:02.597

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That being said, did Descartes ever state why one even has the ability to doubt?

I assume we can all agree that we indubitably have the ability to doubt; it is impossible to doubt that one can doubt. So, we have to take the presence of this ability as a given.

But why we have this ability? To ask this question assumes the Principle of Sufficient Reason (that is to say, that nothing happens without a reason.) Although Descartes doesn't explicitly thematize this principle (the way Leibniz, for example, does) he appears to endorse it insofar as he argues that all things ultimately come from God. (The question of whether or not God is subject to the PSR is another issue altogether, for Descartes.)

So, the implied argument would be: we were created by God, and we have the ability to doubt, so therefore the ability to doubt came from God.

Descartes doesn't (to the best of my knowledge) make this argument explicitly, but it seems pretty easy to connect the dots.

I agree it does seem logical to connect the dots. However, I think curiosity is getting the best of me, as I wonder if Descartes ever doubted his ability to doubt. I suppose, when Descartes states "Cogito ergo sum" (I think therefore I am) it is implied that doubting doubt is NOT reasonable. I assumed he may have provided an argument for his reasoning. Thanks again for a great answer. – E1Suave – 2012-05-04T12:11:25.230

1As I said, I don't think one can reasonably doubt one's ability to doubt, due to the built-in reductio ad absurdam-- if we doubt our ability to doubt, we are already doubting, which proves we are able to doubt. QED – Michael Dorfman – 2012-05-04T13:27:31.303

Aha... got it. Proof by contradiction. Thank you for your patience and additional explanation. – E1Suave – 2012-05-04T13:52:06.967