The first precept was never to accept a thing as true until I knew it as such without a single doubt.
The greatest minds are capable of the greatest vices as well as of the greatest virtues.
The long concatenations of simple and easy reasoning which geometricians use in achieving their most difficult demonstrations gave me occasion to imagine that all matters which may enter the human mind were interrelated in the same fashion.
Travelling is almost like talking with those of other centuries.
It is easy to hate and it is difficult to love. This is how the whole scheme of things works. All good things are difficult to achieve; and bad things are very easy to get.
Nothing is more fairly distributed that common sense: no one thinks he needs more of it than he already has.
I am indeed amazed when I consider how weak my mind is and how prone to error.