“One consideration especially that we ought never to lose from sight,” says Diderot, “is that, if we ever banish a man, or the thinking and contemplative being, from above the surface of the earth, this pathetic and sublime spectacle of nature becomes no more than a scene of melancholy and silence ... It is the presence of man that gives its interest to the existence of other beings ... Why should we not make him a common centre? ... Man is the single term from which we ought to set out.” [Footnote: The passage from Diderot’s article Encyclopedie is given as translated by Morley, Diderot, i, 145.] Hence psychology, morals, the structure of society, were the subjects which riveted attention instead of the larger supra-human problems which had occupied Descartes, Malebranche, and Leibnitz. It mattered little whether the universe was the best that could be constructed; what mattered was the relation of man’s own little world to his will and capacities.
Physical science was important only in so far as it could help social science and minister to the needs of man. The closest analogy to this development of thought is not offered by the Renaissance, to which the description humanistic has been conventionally appropriated, but rather by the age of illumination in Greece in the latter half of the fifth century B.C., represented by Protagoras, Socrates, and others who turned from the ultimate problems of the cosmos, hitherto the main study of philosophers, to man, his nature and his works.
In this revised form of “anthropo-centrism” we see how the general movement of thought has instinctively adapted itself to the astronomical revolution. On the Ptolemaic system it was not incongruous or absurd that man, lord of the central domain in the universe, should regard himself as the most important cosmic creature. This is the view, implicit in the Christian scheme, which had been constructed on the old erroneous cosmology. When the true place of the earth was shown and man found himself in a tiny planet attached to one of innumerable solar worlds, his cosmic importance could no longer be maintained. He was reduced to the condition of an insect creeping on a “tas de boue,” which Voltaire so vividly illustrated in Micromegas. But man is resourceful; [words in Greek]. Displaced, along with his home, from the centre of things, he discovers a new means of restoring his self-importance; he interprets his humiliation as a deliverance. Finding himself in an insignificant island floating in the immensity of space, he decides that he is at last master of his own destinies; he can fling away the old equipment of final causes, original sin, and the rest; he can construct his own chart and, bound by no cosmic scheme, he need take the universe into account only in so far as he judges it to be to his own profit. Or, if he is a philosopher, he may say that, after all, the universe for him is built out of his own sensations, and that by virtue of this relativity “anthropo-centrism” is restored in a new and more effective form.