"If you don't know a number of things, compare them."
Rémi Brague's riff on "if you don't know something, . . . teach it". In "The meaning and value of philosophy in the three medieval cultures," which is chap. 2 of The legend of the Middle Ages: philosophical explorations of medieval Christianity, Judaism, and Islam, trans. Lydia G.Cochrane (Chicago, IL: University of Chicago Press, 2009): 42 (1-22).