Basil L. Gildersleeve, Syntax of Classical Greek

A similar function is exercised in epic and lyric poetry by “κεν” (“κε”), and in Doric by “κα”. The two particles “ἄν” and “κεν” are sometimes combined as “ἄν κεν”. A common origin once suspected is now seldom maintained.¹ The accented “ἄν” may originally have been more clearly demonstrative, the unaccented “κεν” more surely indefinite, but the whole matter is obscure, and a sharp discrimination between “ἄν” and “κεν” often attempted has never been successfully established. “ἄν” is everywhere distinctly preferred in negative sentences, enters more readily into close combinations, and on common ground gradually thrusts “κεν” to the wall. So in Pindar “ἄν” nearly balances “κεν”, whereas in Homer “κεν” greatly preponderates, “κεν” being to “ἄν” in the Iliad as 4 to 1.