Nominalism is the metaphysical philosophy of Nominalists that universals and abstract realities have no real existence, and that their designation as existing realities is a convention of names and language and an illusion. It is opposed to the metaphysical philosophy of Realism. Conceptualism designates several metaphysical doctrines proposing a compromise between realism and nominalism which regard universals as concepts. Compare Idea and Idealism; also Solipsism and Objectivism.