The modern idea that we can know relations only and that there are things in themselves which are unknowable is an old error inherited from mediæval scholasticism, and its roots can be traced back to the philosophy of Aristotle. The difficulty disappears as soon as we consider the whole world (ourselves included) as an interacting whole, and that the conceptions “things” and “relations” have been invented for describing certain of its parts and certain of its interactions or interconnections. If we push the idea of things in themselves to the ultimate extreme we arrive at the atomistic conception of the universe. _Atoms are the things in themselves reduced to the point system._ If we consider the world as a heap of innumerable atoms, we are at a loss how to explain the interaction among these atoms. The atomist universalises the substance-abstraction and will be disappointed afterwards not to be able to deduce from his universalisation other qualities which are found in reality, such as the relations of things, their interconnections, their spontaneity of motion, the life of organised beings, and the mind of thinking creatures. Ideas are symbols and symbols have a meaning. The whole realm of mental representations may be viewed in their symbolism or in their significance. Considering their symbolism, ideas of things as well as of relations, are products of the mind, considering their meaning, ideas represent realities; in other words: their contents or that which they signify is real. It appears that neither Nominalism nor Realism is right; yet if we stretch them only a little, if we are allowed to interpret them in the light of a monistic world-conception, both are right. They cease to be contradictory and become complementary. Universals are real, say the Realists, i. e. the forms and relations of things are actualities. Universals are names, say the Nominalists, i. e. the relations and forms in which we describe the world are mental symbols. The Realists had the misfortune to defeat the Nominalists entirely, and thus had a chance to insist upon being right in every respect. All opposition having ceased, the errors of Realism grew in extraordinary exuberance. Nominalism in the mean time raised its head in opposition to the recognised authority of the church as well as the schools, slowly yet powerfully and irresistibly. The errors and the tyranny of Realism gave strength to the Nominalistic movement which reached its height in Kant’s philosophy. The Realists had gone to the extreme of declaring that universals were things, real substances, independent of single and concrete objects, and the Nominalists on the other hand, represented by Kant, went so far as to declare that all relations, time and space included were _mere_ products of the mind.