The reading of all good books is like a conversation with the finest minds of past centuries.
To know what people really think, pay regard to what they do, rather than what they say.
It is not enough to have a good mind; the main thing is to use it well.
Divide each difficulty into as many parts as is feasible and necessary to resolve it.
Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.
Except our own thoughts, there is nothing absolutely in our power.
I think; therefore I am.
Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has.
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.
Each problem that I solved became a rule, which served afterwards to solve other problems.
Cogito ergo sum. (I think, therefore I am.)
I think; therefore I am.
Everything is self-evident.
Conquer yourself rather than the world.
I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.
When writing about transcendental issues, be transcendentally clear.
When it is not in our power to follow what is true, we ought to follow what is most probable.
Illusory joy is often worth more than genuine sorrow.
In order to improve the mind, we ought less to learn, than to contemplate.
The reading of all good books is indeed like a conversation with the noblest men of past centuries who were the authors of them, nay a carefully studied conversation, in which they reveal to us none but the best of their thoughts.
There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.
It is only prudent never to place complete confidence in that by which we have even once been deceived.
The first precept was never to accept a thing as true until I knew it as such without a single doubt.
I am indeed amazed when I consider how weak my mind is and how prone to error.
Travelling is almost like talking with those of other centuries.
A state is better governed which has few laws, and those laws strictly observed.
I hope that posterity will judge me kindly, not only as to the things which I have explained, but also to those which I have intentionally omitted so as to leave to others the pleasure of discovery.
One cannot conceive anything so strange and so implausible that it has not already been said by one philosopher or another.
The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.
Common sense is the most fairly distributed thing in the world, for each one thinks he is so well-endowed with it that even those who are hardest to satisfy in all other matters are not in the habit of desiring more of it than they already have.
The greatest minds are capable of the greatest vices as well as of the greatest virtues.
The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.
Perfect numbers like perfect men are very rare.