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

My third maxim was to try always to conquer myself rather than fortune, and to change my desires rather than the order of the world, and generally to accustom myself to believing that there is nothing entirely in our power except our thoughts, so that after we have done our best regarding things external to us, everything in which we do not succeed is for us absolutely impossible.

By 'God', I understand, a substance which is infinite, independent, supremely intelligent, supremely powerful, and which created both myself and everything else [...] that exists. All these attributes are such that, the more carefully I concentrate on them, the less possible it seems that they could have originated from me alone. So, from what has been said it must be concluded that God necessarily exists.

It is to the body alone that we should attribute everything that can be observed in us to oppose our reason.

De omnibus dubitandum

He lives well who is well hidden.

Omnia apud me mathematica fiunt.