Man is a rational animal, and if human affairs are hard to regulate, his twofold nature is usually the cause. Reason is something ultimate; it would be the same in another planet, or in another universe, as it is here. Animal nature is something contingent; it might have been different. Our life is a compromise, a blend between the animal and the rational.

Chapter I, "The Problem Profounded", p. 1 - The Economic Problem (1925)