Books are the money of Literature, but only the counters of Science.

Every great advance in natural knowledge has involved the absolute rejection of authority.

Fact I know; and Law I know; but what is this Necessity, save an empty shadow of my own mind's throwing?

Freedom and order are not incompatible... truth is strength... free discussion is the very life of truth.

I am content with nothing, restless and ambitious... and I despise myself for the vanity, which formed half the stimulus to my exertions. Oh would that I were one of those plodding wise fools who having once set their hand to the plough go on nothing doubting.

I do not say think as I think, but think in my way. Fear no shadows, least of all in that great spectre of personal unhappiness which binds half the world to orthodoxy.

I took thought, and invented what I conceived to be the appropriate title of 'agnostic'.

If a little knowledge is dangerous, where is the man who has so much as to be out of danger?

In scientific work, those who refuse to go beyond fact rarely get as far as fact.