There is nothing more ancient than the truth.

I know that I exist; the question is, What is this 'I' that 'I' know.

Sensations are nothing but confused modes of thinking.

Doubt is the origin of wisdom

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

Although my knowledge grows more and more, nevertheless I do not for that reason believe that it can ever be actually infinite, since it can never reach a point so high that it will be unable to attain any greater increase.

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.