Abelard follows Guillaume de Champeaux, with whom he was for the earlier part of his career a contemporary. Confounding, as it would seem, ideas with universals, and universals with abstractions, he denied alike Rosceline's doctrine that they are mere words, and Guillaume de Champeaux's doctrine that they are entities or existences _a parte rei_, and maintained that they are conceptions, really existing _in mente_, but not _in re_. Hence his philosophy is called Conceptualism. He would seem to have held that universals are formed by the mind operating on the concrete objects presented by experience, not, as since maintained by Kant, that they are necessary forms of the understanding. Thus, _humanitas_, humanity, is formed by the mind from the concrete man, or _homo_. There is no humanity _in re_; there are only individual men. In the word humanity the mind expresses the qualities which it observes to be common to all men, without paying attention to any particular man. The idea humanity, then, is simply the abstraction or generalization of these qualities. Abelard, it would appear from this, makes what we call the race a property or quality of individuals, which, of course, excludes the idea of generation. There is, as far as we can see, no essential difference between the conceptualism of Abelard and the nominalism of Rosceline; for, by denying the existence _in re_ of genera and species, and making them only conceptions, it recognizes as really existing only individuals or particulars. St. Thomas Aquinas, than whom no higher authority in philosophy can be named, and from whose conclusions few who understand them will be disposed to dissent, differs from each of these schools, and maintains that universals are conceptions existing _in mente cum fundamento in re_, or conceptions with a basis in reality, which is true of all abstractions; for the mind can form no conceptions except from objects presented by experience. I could form no conception of whiteness if I had no experience of white things, or of roundness if I had seen nothing round. I imagine a golden mountain, but only on condition that gold and mountain are to me objects of experience. This is certain, and accords with the peripatetic maxim, _Nihil est in intellectu, quod prius non fuerit in sensu_, which Leibnitz would amend by adding, _nisi ipse intellectus_, an amendment which, perhaps, contains in germ the whole Kantian philosophy.