First it will be well to set limits to our undertaking, and the important thing in doing this is to cut off all metaphysical questions. We shall not learn, or even inquire, about the ultimate nature of human life: the body-mind problem, the question of free will vs. determinism, what is the highest good, whether there is a conscious purpose back of human existence. These questions belong to philosophy or religion. Science cannot answer them, at least at present, and some scholars grant that it can never answer them. No man has studied the whole realm of science more devotedly than Herbert Spencer, yet he entitled the first part of his Synthetic Philosophy "The Unknowable." Sociology assumes, just as physiology and psychology do, that man is a part of the natural world, that there are uniformities back of what we see or experience in this world, and that we can discover these uniformities by proper methods of study. But there is no assumption that we can know everything, or that there may not be other factors back of those which our science can discover, and other destinies beyond those which our science can predict.

. . . Everything in nature becomes unexplainable if we trace it far enough back. - L. F. Ward, Pure Sociology, pp. 493, 494.

. . . You might liken society to a party of men with lanterns making their way by night through an immeasurable forest. The light which the lanterns throw about each individual, and about the party as a whole, showing them how to guide their immediate steps, may increase indefinitely, illuminating more clearly a larger area; but there will always remain, probably, the plutonian wilderness beyond. - Cooley, Social Process, p. 362.