The philosophical problem to which the mediæval thinkers addressed themselves is one that it is essential to the progress of human thought to solve. Whence do we derive general notions (Universals, as they were called), and do they correspond to anything which actually exists? Thus for the purpose of classifying our knowledge we use certain terms, such as genera, species, and others more technical. Do these in reality exist independently of particular individuals or substances? One school of philosophers, basing their reasoning upon Plato, maintained that such general ideas had a real existence of their own, and hence gained the name of Realists. But another school, who took Aristotle as their champion, held that reality can be asserted of the individual alone, that there is nothing real in the general idea except the name by which it is designated; while some of these Nominalists, as they came to be called, even proclaimed that the parts of an individual whole were mere words, and could not be considered as having an existence of their own. With the application of these definitions to theological dogmas we reach the beginning of Scholastic Theology. Here both sides were soon landed in difficulties. Nominalism, in its denial of reality to general notions, undermined the Catholic idea of the Church: in its recognition of none except individuals it destroyed the whole conception of the solidarity of original sin; while those of its professors who allowed no existence of their own to the parts of an individual whole, resolved the Trinity into three Gods. On the other hand, the danger of Realism was that, since individuals were regarded merely as forms or modes of some general idea, these philosophers were inclined to make no distinction between individuals and to fall into pantheism. As a result, the personality of man, and with it the immortality of the soul, disappeared, and even the personality of God threatened to lose itself in the universe which He had created. These tendencies will be clear from a short account of the chief schoolmen or writers on Scholastic Philosophy. [Sidenote: Roscelin and Anselm.]