But, like the unity of the Church, the doctrine of a universal monarchy had a theoretical as well as an historical basis, and may be traced up to those metaphysical ideas out of which the system we call Realism developed itself. The beginnings of philosophy in those times were logical; and its first efforts were to distribute and classify: system, subordination, uniformity, appeared to be that which was most desirable in thought as in life. The search after causes became a search after principles of classification; since simplicity and truth were held to consist not in an analysis of thought into its elements, nor in an observation of the process of its growth, but rather in a sort of genealogy of notions, a statement of the relations of classes as containing or excluding each other. These classes, genera or species, were not themselves held to be conceptions formed by the mind from phenomena, nor mere accidental aggregates of objects grouped under and called by some common name; they were real things, existing independently of the individuals who composed them, recognized rather than created by the human mind. In this view, Humanity is an essential quality present in all men, and making them what they are: as regards it they are therefore not many but one, the differences between individuals being no more than accidents. The whole truth of their being lies in the universal property, which alone has a permanent and independent existence. The common nature of the individuals thus gathered into one Being is typified in its two aspects, the spiritual and the secular, by two persons, the World-Priest and the World-Monarch, who present on earth a similitude of the Divine unity. For, as we have seen, it was only through its concrete and symbolic expression that a thought could then be apprehended[112]. Although it was to unity in religion that the clerical body was both by doctrine and by practice attached, they found this inseparable from the corresponding unity in politics. They saw that every act of man has a social and public as well as a moral and personal bearing, and concluded that the rules which directed and the powers which rewarded or punished must be parallel and similar, not so much two powers as different manifestations of one and the same. That the souls of all Christian men should be guided by one hierarchy, rising through successive grades to a supreme head, while for their deeds they were answerable to a multitude of local, unconnected, mutually irresponsible potentates, appeared to them necessarily opposed to the Divine order. As they could not imagine, nor value if they had imagined, a communion of the saints without its expression in a visible Church, so in matters temporal they recognized no brotherhood of spirit without the bonds of form, no universal humanity save in the image of a universal State[113]. In this, as in so much else, the men of the Middle Ages were the slaves of the letter, unable, with all