If I found any new truths in the sciences, I can say that they follow from, or depend on, five or six principal problems which I succeeded in solving and which I regard as so many battles where the fortunes of war were on my side.

And I shall always hold myself more obliged to those by whose favour I enjoy uninterrupted leisure than to any who might offer me the most honourable positions in the world.

This result could have been achieved either by his [God] endowing my intellect with a clear and distinct perception of everything about which I would ever deliberate, or simply by impressing the following rule so firmly upon my memory that I could never forget it: I should never judge anything that I do not clearly and distinctly understand.

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.

It's the familiar love-hate syndrome of seduction: "I don't really care what it is I say, I care only that you like 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.

[About Pierre de Fermat] It cannot be denied that he has had many exceptional ideas, and that he is a highly intelligent man. For my part, however, I have always been taught to take a broad overview of things, in order to be able to deduce from them general rules, which might be applicable elsewhere.