... moral certainty is certainty which is sufficient to regulate our behaviour, or which measures up to the certainty we have on matters relating to the conduct of life which we never normally doubt, though we know that it is possible, absolutely speaking, that they may be false.

Here I beg you to observe in passing that the scruples that prevented ancient writers from using arithmetical terms in geometry, and which can only be a consequence of their inability to perceive clearly the relation between these two subjects, introduced much obscurity and confusion into their explanations.

We never understand a thing so well,and make it our own, as when we have discovered it for ourselves.

Common sense is the most widely shared commodity in the world, for every man is convinced that he is well supplied with it.

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

Archimedes, that he might transport the entire globe ... demanded only a point that was firm and immovable; so also, I shall be entitled to entertain the highest expectations, if I am fortunate enough to discover only one thing that is certain and indubitable.

But in my opinion, all things in nature occur mathematically.