what characterizes man is the richness and subtlety, the variety and versatility of his nature….Rational thought, logical and metaphysical thought can comprehend only those objects which are free from contradiction, and which have a consistent nature and truth. It is, however, just this homogeneity which we never find in man. The philosopher is not permitted to construct an artificial man; he must describe a real one. All the so-called definitions of man are nothing but airy speculation so long as they are not based upon and confirmed by our experience of man. There is no other way to know man than to understand his life and conduct. But what we find here defies every attempt at inclusion within a single and simple formula. Contradiction is the very element of human existence. Man has no ‘nature’—no simple or homogeneous being.