=Growth of Theory from Practical Problems.=--Of one thing we may be sure. If inquiries are to have any substantial basis, if they are not to be wholly up in the air, the theorist must take his departure from the problems which men actually meet in their own conduct. He may define and refine these; he may divide and systematize; he may abstract the problems from their concrete contexts in individual lives; he may classify them when he has thus detached them; but if he gets away from them he is talking about something which his own brain has invented, not about moral realities. On the other hand, the perplexities and uncertainties of direct and personal behavior invite a more abstract and systematic impersonal treatment than that which they receive in the exigencies of their occurrence. The recognition of any end or authority going beyond what is embodied in existing customs, involves some appeal to thought, and moral theory makes this appeal more explicit and more complete. If a child asks why he should tell the truth, and is answered, "because you ought to and that is reason enough"; or, "because it will prove profitable for you to do so"; or, "because truth-telling is a condition of mutual communication and common aims," the answer implies a principle which requires only to be made explicit to be full-fledged theory. And when this principle is compared with those employed in other cases to see if they are mutually consistent; and if not, to find a still more fundamental reconciling principle, we have passed over the border into ethical system.