On 07 May 1879, Charles Darwin wrote a letter of reply to Sir John Fordyce, an atheist, in which Darwin states that he thinks it is absurd to doubt that a man may be an ardent theist and an evolutionist at the same time. He says that he has never considered himself an atheist “in the sense of denying the existence of God,” but rather he would qualify himself as an agnostic. Here is the letter:
Down Beckenham | Kent
May 7 1879
It seems to me absurd to doubt that a man may be an ardent Theist & an evolutionist.— You are right about Kingsley. Asa Gray, the eminent botanist, is another case in point— What my own views may be is a question of no consequence to any one except myself.— But as you ask, I may state that my judgment often fluctuates. Moreover whether a man deserves to be called a theist depends on the definition of the term: which is much too large a subject for a note. In my most extreme fluctuations I have never been an atheist in the sense of denying the existence of a God.—
I think that generally (& more and more so as I grow older) but not always, that an agnostic would be the most correct description of my state of mind.
Dear Sir, Yours faithfully