_(a) Delusions._—In primitive conditions the most common delusion is that of the identity of waking and dream-life. There is no distinction allowed in the equal reality of both, or, if any, it is in favour of the superiority of the dream-life, for in dreams the person seems possessed of powers which he loses on awakening. So highly are dreams esteemed, that many savage tribes and many nations of respectable culture have risked their gravest undertakings on the interpretation of these visions of the night. Such a delusion is, of course, most contrary to reason and good order. On account of an inauspicious dream a Brazilian tribe will desert its village and its plantations; while if a Kamchatkan dreams that he has been given another man’s wife, it is held necessary for public welfare that his dream be realised. Another delusion, deeply rooted in the philosophy of India and which has worked untold misfortunes on its peoples, is that of the unreality of the distinction between subject and object—that is, between thought and the external world. Hence arose the doctrine that real life is _mâyâ_, an illusion or deception of the senses, and its aims and duties unworthy the contemplation of the true philosopher. The consequent neglect of the practical duties of life could not fail to weaken the peoples who juggled with sound reason in this manner. A wonderful example of long-persistent delusion was the Crusades. For nearly two centuries (1095–1289) the Christian nations of Europe neglected state and domestic affairs in order to rescue the Holy Sepulchre from the hands of the infidels. All classes, from kings to peasants, fell a prey to the same obsession. It was accompanied by repeated and unmistakable signs of epidemic manias and neuropathias unequalled in history. Lykanthropy, in which the possessed howled and destroyed like wolves, was extremely common; the dancing mania spread through wide areas, forcing old and young into wild gestures and crazy motions; and, stranger than all, young children were attacked with a mad desire to leave their homes and to wander forth they knew not whither. Were they prevented, they pined and died. These “children’s crusades” began in Germany in 1212, extended through France, Switzerland, and Italy, and continued as late as 1418. _(b) Dominant Ideas._—The weightiest topic in universal history may possibly be the study of dominant or fixed ideas in ethnic psychology. A philosophic observer may regard each nation as the destined representative of some one idea, which, when its usefulness has ended, yields to others more germane to existing conditions; and by the successive action of all, the progress of the species is secured through the gradual elimination of those which are regressive.