“Man of Letters: A well-educated, well-read, civilized and perhaps learned person—who may also be a writer (e.g. a belle-lettrist). ‘A man of capital letters,’ on the other hand, is one who thinks he is these things but is, in fact, very limited. Pope’s victims in The Dunciad might be called ‘men of capital letters’. See also BELLES LETTRES; LITERATI.”
Excerpted from: Cuddon, J.A. The Penguin Dictionary of Literary Terms and Literary Theory. New York: Penguin, 1992.