Cassirer counts history as a symbolic form in his list that includes myth, religion, language, art, and science, but his discussion of history is confined to a chapter in An Essay on Man. A more complete understanding requires attention to a year-long seminar he taught at Yale on "The Philosophy of History" in 1941-1942. The partially unpublished texts of this seminar are the most extended exposition of Cassirer's conception of history as a symbolic form. The key source for Cassirer's philosophy of history is Vico. Cassirer holds that "historical consciousness" is a very late product of human civilization not found before the Greeks and even with the Greeks history is not analyzed as a particular form of thought. Cassirer claims that such analysis did not appear until the eighteenth century in the work of Vico and Herder.