Bad books engender bad habits, but bad habits engender good books..

These long chains of perfectly simple and easy reasonings by means of which geometers are accustomed to carry out their most difficult demonstrations….

Give me extension and motion and I will construct the universe..

How can you be certain that your whole life is not a dream?.

When I consider this carefully, I find not a single property which with certainty separates the waking state from the dream. How can you be certain t….

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

The first precept was never to accept a thing as true until I knew it as such without a single doubt..

With me, everything turns into mathematics..

Mathematics is a more powerful instrument of knowledge than any other that has been bequeathed to us by human agency..

... moral certainty is certainty which is sufficient to regulate our behaviour, or which measures up to the certainty we have on matters relating to ….

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 wh….

When writing about transcendental issues, be transcendentally clear..

Whatever I have up till now accepted as most true and assured I have gotten either from the senses or through the senses. But from time to time I hav….

So far, I have been a spectator in this theater which is the world, but I am now about to mount the stage, and I come forward masked..

In order to improve the mind, we ought less to learn, than to contemplate..

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..

Doubt is the origin of wisdom.

Every man is indeed bound to do what he can to promote the good of others, and a man who is of no use to anyone is strictly worthless..

Travelling is almost like talking with those of other centuries..

Perfect numbers like perfect men are very rare..

If I simply refrain from making a judgment in cases where I do not perceive the truth with sufficient clarity and distinctness, then it is clear that….