Even if I doubt everything, I cannot doubt that I think.

Supports

Let us push as far as it will go: grant that an evil demon deceives me about the world, about my body, about the very truths of mathematics.
But to be deceived, I must still think; and if I think, I exist, at least as a thinking thing. To be wrong even about this would still require that I think.
The proposition "I am, I exist" is therefore true each time I frame it: doubt, far from shaking it, confirms it with every attempt to deny it.

Therefore Therefore there exists at least one indubitable truth: doubt has a limit, and knowledge a definitive foothold.

How far does this reasoning convince you?

Not at all

Entirely

Deepenings

From the cogito to the criterion of evidence

What makes the cogito irresistible, Descartes says, is that I conceive it clearly and distinctly: no obscurity in it leaves a hold for doubt.
Now if evidence is the mark of the true in this case, it can be so elsewhere: whatever I conceive just as clearly merits the same certainty. The cogito is not an exception, it is a model.

How far does this reasoning convince you?

Not at all

Entirely

Put to the test

Problem