Variant: When it is not in our power to follow what is true, we ought to follow what is most probable.

The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.

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.

Even those who have the weakest souls could acquire absolute mastery over all their passions if we employed sufficient ingenuity in training and guiding them.

Here I beg you to observe in passing that the scruples that prevented ancient writers from using arithmetical terms in geometry, and which can only be a consequence of their inability to perceive clearly the relation between these two subjects, introduced much obscurity and confusion into their explanations.

Divide each difficulty at hand into as many pieces as possible and as could be required to better solve them.

The principal effect of the passions is that they incite and persuade the mind to will the events for which they prepared the body.