William of Ockham was a pioneer of nominalism, and some consider him the father of modern epistemology, because of his strongly argued position that only individuals exist, rather than supra-individual universals, essences, or forms, and that universals are the products of abstraction from individuals by the human mind and have no extra-mental existence. He denied the real existence of metaphysical universals and advocated the reduction of ontology. William of Ockham is sometimes considered an advocate of conceptualism rather than nominalism, for whereas nominalists held that universals were merely names, i.e. words rather than extant realities, conceptualists held that they were mental concepts, i.e. the names were names of concepts, which do exist, although only in the mind. Therefore, the universal concept has for its object, not a reality existing in the world outside us, but an internal representation which is a product of the understanding itself and which "supposes" in the mind the things to which the mind attributes it; that is, it holds, for the time being, the place of the things which it represents. It is the term of the reflective act of the mind. Hence the universal is not a mere word, as Roscelin taught, nor a sermo, as Peter Abelard held, namely the word as used in the sentence, but the mental substitute for real things, and the term of the reflective process. For this reason William has sometimes also been called a "Terminist", to distinguish him from a nominalist or a conceptualist.
