Darwin's religious thinking
Dear Sir
It seems to me absurd to doubt that a man may be an ardent Theist & an evolutionist. [...] What my own views may be is a question of no consequence to anyone 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.
Yours faithfully.
Ch. Darwin
Letter from Charles Darwin to John Fordyce*, 7 May 1879, Darwin Correspondence Project Source : http://www.darwinproject.ac.uk
*John Fordyce is the author of Aspects of Scepticism. With special reference to the present time, 1883.