=The Problem of Individuality――The Relation of Particulars and Universals.= The all-absorbing question of the Transitional Period, of the relation of particulars and universals, became for Thomas and his successors the problem of individuality. For the schoolman was obliged to define the individual and fix his place in his Aristotelian world, if he was to be successful against the pantheism of the Arabian Aristotelianism. What is the nature and standing of the individual? What constitutes the difference between individuals? The whole theological edifice of Thomas would collapse in mystic unity, the immortality of the soul would be lost and the offices of the church would be nullified, unless Thomas showed the positive nature of the individual. In this connection we must remember that on the whole the Middle Ages had accepted Abelard’s analysis of the problem of the relation of universals and particulars: the universals exist in three ways, _ante rem_ or in God’s mind; _post rem_ or in man’s mind; _in re_ or in nature. To Thomas the universals as abstractions (_universalia post rem_) in the human mind cannot be individuals, for they have no real existence. To have real existence the universal must exist _in re_, in the many, as the essence of things; not as abstraction _beside_ the many. The question of individuality therefore to Thomas concerns properly only objects _in re_, or objects in the corporeal world.[65] These are objects of Form and Matter. The question is, whether the Form or the matter of corporeal things is the principle of its individuality. Thomas says that matter is this principle,――not indeterminate matter, but matter with quantitative determinations. The difference between earthly individuals is numerical――a difference of time and space relations. The Forms of nature objects change continually according to their material conditions, but these conditions do not change. Nevertheless the quantitative determinations of individuals are not the cause, but the condition, of their existence.