Cogito ergo sum. (I think, therefore I am.)

entre plusieurs opinions également reçues, je ne choisissais que les plus modérées, tant à cause que ce sont toujours les plus commodes pour la pratique, et vraisemblablement les meilleures, tous excès ayant coutume d'être mauvais, comme aussi afin de me détourner moins du vrai chemin, en cas que je faillisse, que si, ayant choisi l'un des extrêmes, c'eût été l'autre qu'il fallu suivre. (3e partie, para 2)

I am thinking, therefore I exist. (...) I was a substance whose whole essence or nature is solely to think, and which does not require any place, or depend on any material thing, in order to exist. Accordingly this 'I' - that is, the soul by which I am what I am - is entirely distinct from the body, and indeed is easier to know than the body, and would not fail to be whatever it is, even if the body did not exist.

I can doubt everything, except one thing, and that is the very fact that I doubt. Simply put - I think, therefore I am

Common sense is the best distributed thing in the world, for we all think we possess a good share of it.

Everybody thinks himself so well supplied with common sense that even those most difficult to please. . . never desire more of it than they already have.

Instead I ought to be grateful to Him who never owed me anything for having been so generous to me, rather than think that He deprived me of those things or has taken away from me whatever He did not give me.

I think therefore am.

Good sense is, of all things among men, the most equally distributed; for every one thinks himself so abundantly provided with it, that those even who are the most difficult to satisfy in everything else, do not usually desire a larger measure of this quality than they already possess.