The two operations of our understanding, intuition and deduction, on which alone we have said we must rely in the acquisition of knowledge.
— Rene Descartes
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.
There is nothing so strange and so unbelievable that it has not been said by one philosopher or another.
Illusory joy is often worth more than genuine sorrow.
An optimist may see a light where there is none, but why must the pessimist always run to blow it out?
I think; therefore I am.
Travelling is almost like talking with those of other centuries.
Each problem that I solved became a rule, which served afterwards to solve other problems.
The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.
One cannot conceive anything so strange and so implausible that it has not already been said by one philosopher or another.
The greatest minds are capable of the greatest vices as well as of the greatest virtues.
In order to improve the mind, we ought less to learn, than to contemplate.
Whenever anyone has offended me, I try to raise my soul so high that the offense cannot reach it.
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.
I am accustomed to sleep and in my dreams to imagine the same things that lunatics imagine when awake.
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.
Divide each difficulty into as many parts as is feasible and necessary to resolve it.
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 is only prudent never to place complete confidence in that by which we have even once been deceived.
A state is better governed which has few laws, and those laws strictly observed.
Everything is self-evident.
Nothing is more fairly distributed than common sense: no one thinks he needs more of it than he already has.
When it is not in our power to follow what is true, we ought to follow what is most probable.
It is not enough to have a good mind; the main thing is to use it well.
Perfect numbers like perfect men are very rare.
The reading of all good books is like a conversation with the finest minds of past centuries.
Except our own thoughts, there is nothing absolutely in our power.
