In metaphysics, conceptualism is a theory that explains universality of particulars as conceptualized frameworks situated within the thinking mind. Intermediate between nominalism and realism, the conceptualist view approaches the metaphysical concept of universals from a perspective that denies their presence in particulars outside the mind's perception of them. Conceptualism is anti-realist about abstract objects, just like immanent realism is (their difference being that immanent realism accepts there are mind-independent facts about whether universals are instantiated).

The evolution of late scholastic terminology has led to the emergence of conceptualism, which stemmed from doctrines that were previously considered to be nominalistic. The terminological distinction was made in order to stress the difference between the claim that universal mental acts correspond with universal intentional objects and the perspective that dismissed the existence of universals outside the mind. The former perspective of rejection of objective universality was distinctly defined as conceptualism.

Peter Abélard was a medieval thinker whose work is currently classified as having the most potential in representing the roots of conceptualism. Abélard’s view denied the existence of determinate universals within things. William of Ockham was another famous late medieval thinker who had a strictly conceptualist solution to the metaphysical problem of universals. He argued that abstract concepts have no fundamentum outside the mind.

In the 17th century conceptualism gained favour for some decades especially among the Jesuits: Pedro Hurtado de Mendoza, Rodrigo de Arriaga and Francisco Oviedo are the main figures. Although the order soon returned to the more realist philosophy of Francisco Suárez, the ideas of these Jesuits had a great impact on the early modern philosophy.

Conceptualism was either explicitly or implicitly embraced by most of the early modern thinkers, including René Descartes, John Locke, Baruch Spinoza, Gottfried Wilhelm Leibniz, George Berkeley, and David Hume – often in a quite simplified form if compared with the elaborate scholastic theories.

Sometimes the term is applied even to the radically different philosophy of Immanuel Kant, who holds that universals have no connection with things as they are in themselves because they (universals) are exclusively produced by our a priori mental structures and functions, even though the categories have an objective validity for objects of experience (that is, phenomena).

In late modern philosophy, conceptualist views were held by G. W. F. Hegel.

In contemporary times, Edmund Husserl's philosophy of mathematics has been construed as a form of conceptualism.