The whole interest of reason, speculative as well as practical, is
centred in the three following questions: 1. What can I know? 2. What
ought I to do? 3. What may I hope?
-- Immanuel Kant.
Critique of Pure Reason (1781; 1787)
Chapter II. "The Canon of Pure Reason"
(translated by J. M. D. Meiklejohn)