It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty. This is what Agnosticism asserts; and, in my opinion, it is all that is essential to Agnosticism. That which Agnostics deny and repudiate, as immoral, is the contrary doctrine, that there are propositions which men ought to believe without logically satisfactory evidence; and that reprobation ought to attach to the profession of disbelief in such inadequately supported propositions.

In the world of letters, learning and knowledge are one, and books are the source of both; whereas in science, as in life, learning and knowledge are distinct, and the study of things, and not of books, is the source of the latter.

... our "Physick" and "Anatomy" have embraced such infinite varieties of being, have laid open such new worlds in time and space, have grappled, not unsuccessfully, with such complex problems, that the eyes of Vesalius and of Harvey might be dazzled by the sight of the tree that has grown out of their grain of mustard seed.

'Infidel' is a term of reproach, which Christians and Mohammedans, in their modesty, agree to apply to those who differ from them.

I take it that the good of mankind means the attainment, by every man, of all the happiness which he can enjoy without diminishing the happiness of his fellow men

There is nothing of permanent value (putting aside a few human affections) nothing that satisfies quiet reflection--except the sense of having worked according to one's capacity and light to make things clear and get rid of cant and shams of all sorts.

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