Conceptualism

Conceptualism is a doctrine in philosophy intermediate between nominalism and realism that says universals exist only within the mind and have no external or substantial reality.

Conceptualism in scholasticism
In late and "second" scholasticism, the doctrines that would now be classified as conceptualist were called either moderate nominalism or seminominalism. By means of the late scholastic terminology, conceptualism can be defined as belief in universal formal concepts (resulting by means of formal precision) and rejection of objective concepts (resulting, supposedly, by means of objective precision). In other words, moderate realism and conceptualism both agree in admitting universal mental acts (formal concepts), but differ in that moderate realism claims that to such acts correspond universal intentional objects, whereas conceptualism denies any such universal objects.

In the medieval thought, the first conceptualist was probably Peter Abélard, but some thinkers classify him as a moderate realist. The bulk of late medieval thinkers usually called "nominalists" were in fact conceptualists: William Ockham, Jean Buridan, etc.. In the 17th century conceptualism gained favour for some decades especially among the Jesuits: 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 contemporary early modern thinkers.

Modern conceptualism
Conceptualism was either explicitly or implicitly embraced by most of the early modern thinkers like René Descartes, John Locke or Gottfried Leibniz -- 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 Kant, who holds that universals have no connection with external things because they are exclusively produced by our a priori mental structures and functions. However, this application of the term "conceptualism" is not very usual, since the problem of universals can, strictly speaking, be meaningfully raised only within the framework of the traditional, pre-Kantian epistemology.