I believe there exists, & I feel within me, an instinct for the truth, or knowledge or discovery, of something of the same nature as the instinct of virtue, & that our having such an instinct is reason enough for scientific researches without any practical results ever ensuing from them.

You don't know what you don't know.

You never know a line is crooked unless you have a straight one to put next to it.

All that I know is nothing - I'm not even sure of that.

Books are infinite in number and time is short. The secret of knowledge is to take what is essential. Take that and try to live up to it.

Anything more than the truth would have seemed too weak.