Never undertake anything unless you have the heart to ask Heaven's blessing on your undertaking.

There are very many people who read simply to prevent themselves from thinking.

To write brashly about some things, it is almost necessary not to know much about them.

Be attentive, feel nothing in vain, measure and compare: this is the whole law of philosophy.

One must judge men not by their opinions, but by what their opinions have made of them.

Delight at having understood a very abstract and obscure system leads most people to believe in the truth of what it demonstrates.

We have to believe that everything has a cause, as the spider spins its web in order to catch flies. But it does this before it knows there are such things as flies.