own species, we learned that human beings are inevitably a part of nature and not outside it; in structure, development, and palaeontological history, mankind is subject to the control of the uniform laws which operate throughout the entire range of living things.  Finally, the mental characters and the social relations of human organisms were derived from beginnings lower down in the scale, and were proved to be no more exceptional than the physical constitution of a single human being.

Are we to forget all of these things when we try to put in order our ideas belonging to the categories of higher thought?  Can we hope to find the truth if we fail to employ the methods of scientific common-sense which only yield sure results?  It is no more justifiable to discard our hard-earned knowledge than it would be for an advocate to undertake the conduct of a case in deliberate disregard of what he had learned of the law, or for a surgeon to leave his knowledge at the door when he entered the operating room.  Too often we are bidden to view the larger conceptions of nature and supernature as something outside the realm of ordered knowledge too frequently we are given statements upon authority that takes no account of reason, and we are asked to accept these views whether or not they accord with the demonstrated facts of common-sense.  But those who have followed the present description of evolution can readily recognize their obligation to use for the further analysis of higher human life the means which have given in that doctrine the most reasonable explanation of the natural phenomena already investigated.

I need hardly say that we now enter upon the most difficult stage of our progress.  The regions we have traversed were more readily explored because they were remote from the matters now before us; even in the case of man’s mental and social evolution it was possible to take a partially impersonal view of certain of the essential elements in human life, which we cannot do now.  For ethics and religion and philosophy are groups of ideas that are familiar to us as the property of mankind alone.  Countless obstacles are in the way.  Much mental inertia must be overcome, for it is far easier to accept the average and traditional judgments of other men—­to let well enough alone—­than it is to win our own way to the heights from which we may survey knowledge more fully.  Human prejudices confront us as a veritable jungle, hemming us in and obstructing our vision on all sides; and perhaps much underbrush must be cut away if we are to see widely and wisely.  Nevertheless, to those imbued with a desire to learn truth, anything and everything gained must surely repay a thousand times all efforts to obtain clearness of vision and breadth of view.  With our perspective thus rectified by our backward glance, we turn to the three divisions of human thought now to be examined.  The conceptions of ethics come first for reasons that must be apparent from the classification of the facts