The historian who would fulfil his mission in its amplest sense must trace his facts back to the ideas which gave them birth; he must recognize and define these as the properties of specific peoples; and he must estimate their worth by their tendency to national preservation or national destruction. This is the maxim, the axiom, if you please, which both the ethnologist and the historian must bear ever present in mind if they would comprehend the meaning of institutions or the significance of events. They must be referred to, and explained by, the ideas which gave them birth. As an American historian has tersely put it, "The facts relating to successive phases of _human thought_ constitute History."[18-2] I am aware that a strong school of modern philosophers will present the objection that thought itself is but a necessary result of chemical and mechanical laws, and therefore that it cannot be an independent cause. Dr. Post has pointedly expressed this position in the words: "We do not think; thinking goes on within us,"[19-1] just as other functions, such as circulation and secretion, go on. It is not possible for me at this time to enter into this branch of the discussion. But I may ask your attention to the fact that one of the highest authorities on the laws of natural science, the late George J. Romanes, reached by the severest induction an exactly opposite opinion, which he announced in these words: "The human mind is itself a causal agent. Its motives are in large part matters of its own creation. * * * Intelligent volition is a true cause of adjustive movement."[19-2] For myself, after what I have endeavored to make an unbiased study of both opinions, I subscribe unhesitatingly to the latter, and look upon Mind not only as a potent but as an independent cause of motion in the natural world, of action in the individual life, and, therefore, of events in the history of the species. Confining ourselves to ethnology and history, the causative idea, as I have said, makes itself felt through ethnic ideals. These are influential in proportion as they are vividly realized by the national genius; and elevating in proportion as they partake of those final truths already referred to, which are all merely forms of expression of right reasoning. These ideals are the _idola fori_, which have sometimes deluded, sometimes glorified, those who believed in them. I shall mention a few of them to make my meaning more apparent. That with which we are most familiar in history is the warrior ideal, the personification of military glory and martial success. It is present among the rudest tribes, and that it is active to-day, events in recent European history prove only too clearly; and among ourselves, little would be needed to awaken it to vivid life.