Medieval realism is the philosophical position, debated extensively in medieval European scholasticism, that universals - general terms such as “humanity,” “redness,” or “animality” - have some form of real existence independent of the particular things that instantiate them and independent of the human mind that conceives them. The term is used in contrast to nominalism, which holds that universals are merely names or mental concepts, and to conceptualism, which locates universals in the mind without granting them extramental existence. The precise nature of what “real existence” means in this context was itself a matter of sustained dispute among medieval thinkers, and the boundaries between realist, conceptualist, and nominalist positions are contested in contemporary scholarship.

Medieval realism is studied primarily as a chapter in the history of philosophy and logic, with scholars tracing its development from late ancient sources - particularly Porphyry's Isagoge and Boethius's commentaries on it - through the high scholastic synthesis of the thirteenth century and into the fourteenth-century challenges associated with William of Ockham and his successors. The central question inherited from antiquity, known as the problem of universals, asks whether genera and species exist in reality, whether they are corporeal or incorporeal, and whether they exist apart from sensible things or only within them. Medieval thinkers debated these questions within a broadly Christian theological context, which gave the dispute additional stakes: positions on universals bore on the doctrines of the Trinity, the reality of divine ideas, and the metaphysical status of created kinds.

The realist tradition in the medieval period is generally divided between stronger and weaker forms. Extreme or “ultra-realism,” associated in the eleventh and twelfth centuries with figures such as William of Champeaux, held that a single universal nature is wholly and identically present in each of its particulars. Moderate realism, associated above all with Thomas Aquinas following Aristotle and Avicenna, holds that universals exist in things as their common natures but are abstracted and rendered universal only by the intellect. Between these positions, thinkers such as John Duns Scotus developed intermediate accounts positing a “formal distinction” between a thing's individual and common aspects.

Opposition to realism crystallized most sharply in the work of Roscelin of Compiègne in the late eleventh century, who is traditionally credited with an early nominalist position holding that universals are mere vocal sounds (voces), and in the more developed terminism of William of Ockham in the fourteenth century, who argued that universals are mental signs with no correlate outside the mind. The debate between realists and their critics shaped the curriculum of medieval universities and contributed to the development of formal logic, philosophy of language, and metaphysics as distinct disciplines.

Contemporary historians of philosophy debate how sharply the realist-nominalist distinction should be drawn, whether figures such as Peter Abelard are best classified as nominalists, conceptualists, or something else, and how much continuity exists between medieval and early modern treatments of the problem.

• Extreme realism: Universals exist as single, shared natures fully present in each particular instance. Associated with early medieval Platonizing tendencies and with William of Champeaux before his revision. Discussed at realism-medieval-extreme-realism-viewpoint.

• Moderate realism: Universals exist in things as real common natures but are universalized only through intellectual abstraction; they have no existence prior to or apart from particulars except in the divine intellect. Associated with Aquinas and the Aristotelian mainstream. Discussed at realism-medieval-moderate-realism-viewpoint.

• Scotist realism: A formal distinction, less than a real distinction but more than a merely conceptual one, obtains between an individual's common nature and its individuating principle (haecceity). Associated with John Duns Scotus. Discussed at realism-medieval-scotist-realism-viewpoint.

• Nominalism: Universals are names, terms, or mental concepts and have no extramental reality; only individual things exist. Associated with Roscelin, Ockham, and the via moderna. Discussed at realism-medieval-nominalism-viewpoint.

• Conceptualism: Universals exist as genuine concepts in the mind that are objectively grounded in resemblances among particulars, without themselves being real extramental entities. Associated with Peter Abelard and some readings of Ockham. Discussed at realism-medieval-conceptualism-viewpoint.

• The trial of Roscelin: Roscelin's nominalist position on universals was condemned at the Council of Soissons (1092) partly on the grounds that it was held to entail tritheism in Trinitarian theology; the episode raises questions about the relationship between philosophical positions and ecclesiastical authority in the medieval period. realism-medieval-roscelin-condemnation-controversy

• Ockham's razor and the via moderna: The rapid spread of Ockhamist nominalism in fourteenth- and fifteenth-century universities provoked institutional condemnations and prohibitions at Paris and elsewhere, generating a documented conflict between adherents of the via antiqua (realism) and the via moderna (nominalism) with identifiable parties and lasting institutional consequences. realism-medieval-via-moderna-controversy

• realism-medieval-history - History of the problem of universals in medieval philosophy
• realism-medieval-extreme-realism-viewpoint - Extreme realist position
• realism-medieval-moderate-realism-viewpoint - Moderate realist position
• realism-medieval-scotist-realism-viewpoint - Scotist formal distinction
• realism-medieval-nominalism-viewpoint - Nominalist position
• realism-medieval-conceptualism-viewpoint - Conceptualist position
• realism-medieval-realism-nominalism-debate - Structured exchange between realism and nominalism
• realism-medieval-roscelin-condemnation-controversy - Condemnation of Roscelin at Soissons
• realism-medieval-via-moderna-controversy - Institutional conflict between via antiqua and via moderna
• realism-medieval-haecceity-debate - Debate over Scotus's formal distinction and haecceity
• Problem Of Universals - The broader philosophical problem across periods
• Nominalism - Nominalist positions generally
• Scholasticism - The broader medieval academic tradition
• William of Ockham - Principal nominalist critic of realism
• Roscelin - Early nominalist figure

1. Porphyry, Isagoge, trans. Edward W. Warren (Toronto: Pontifical Institute of Mediaeval Studies, 1975). The three questions Porphyry declines to answer open the medieval debate. 2. Boethius, In Isagogen Porphyrii Commenta, ed. Samuel Brandt, Corpus Scriptorum Ecclesiasticorum Latinorum 48 (Vienna: Tempsky, 1906). 3. Martin M. Tweedale, Abailard on Universals (Amsterdam: North-Holland, 1976). On Abelard's position and its classification. 4. John Marenbon, Medieval Philosophy: An Historical and Philosophical Introduction (London: Routledge, 2007), 76-100. Overview of the problem of universals in the medieval period. 5. Jorge J. E. Gracia, Individuation in Scholasticism: The Later Middle Ages and the Counter-Reformation (Albany: State University of New York Press, 1994). On the realist tradition and individuation. 6. Marilyn McCord Adams, William Ockham, 2 vols. (Notre Dame: University of Notre Dame Press, 1987). Comprehensive treatment of Ockham's nominalism. 7. Constant J. Mews, “Nominalism and Theology before Abaelard: New Light on Roscelin of Compiègne,” Vivarium 30, no. 1 (1992): 4-33. 8. Edith Sylla, “The Oxford Calculators,” in The Cambridge History of Later Medieval Philosophy, ed. Norman Kretzmann, Anthony Kenny, and Jan Pinborg (Cambridge: Cambridge University Press, 1982), 540-563. 9. William J. Courtenay, Schools and Scholars in Fourteenth-Century England (Princeton: Princeton University Press, 1987). On the institutional conflict between via antiqua and via moderna. 10. Timothy B. Noone, “Universals and Individuation,” in The Cambridge Companion to Duns Scotus, ed. Thomas Williams (Cambridge: Cambridge University Press, 2003), 100-128. On Scotus's formal distinction.