But it is more than a personal unity which holds together the thinking of a philosopher. There is the unity of the problem, which the philosopher has always before him, and in which all particular ideas find their unity. All else issues from this and merges into it. The various influences which we have seen affecting Leibniz, therefore, got their effectiveness from the relation which he saw them bear to the final problem of all thought. This is the inquiry after the unity of experience, if we look at it from the side of the subject; the unity of reality, if we put it from the objective side. Yet each age states this problem in its own way, because it sees it in the light of some difficulty which has recently arisen in consciousness. At one time, the question is as to the relation of the one to the many; at another, of the relation of the sensible to the intelligible world; at another, of the relation of the individual to the universal. And this last seems to have been the way in which it specifically presented itself to Leibniz. This way of stating it was developed, though apparently without adequate realization of its meaning, by the philosophy of scholasticism. It stated the problem as primarily a logical question,--the relation of genera, of species, of individuals to each other. And the school-boy, made after the stamp of literary tradition, knows that there were two parties among the Schoolmen,--the Realists, and the Nominalists; one asserting, the other denying, the objective reality of universals. To regard this discussion as useless, is to utter the condemnation of philosophy, and to relegate the foundation of science to the realm of things not to be inquired into. To say that it is an easy matter to decide, is to assume the decision with equal ease of all the problems that have vexed the thought of humanity. To us it seems easy because we have bodily incorporated into our thinking the results of both the realistic and the nominalistic doctrines, without attempting to reconcile them, or even being conscious of the necessity of reconciliation. We assert in one breath that the individual is alone real, and in the next assert that only those forms of consciousness which represent something in the universe are to be termed knowledge. At one moment we say that universals are creations of the individual mind, and at the next pass on to talk of laws of nature, or even of a reign of law. In other words, we have learned to regard both the individual and the universal as real, and thus ignoring the problem, think we have solved it.