John Duns Scotus OFM (/ˈskoʊtəs/ SKOH-təs; Ecclesiastical Latin: [duns ˈskɔtus], "Duns the Scot"; c. 1265/66 – 8 November 1308) was a Scottish Catholic priest and Franciscan friar, university professor, philosopher and theologian. He is one of the four most important Christian philosopher-theologians of Western Europe in the High Middle Ages, together with Thomas Aquinas, Bonaventure and William of Ockham.
Duns Scotus has had considerable influence on both Catholic and secular thought. The doctrines for which he is best known are the "univocity of being", that existence is the most abstract concept we have, applicable to everything that exists; the formal distinction, a way of distinguishing between different formalities of the same thing; and the idea of haecceity, the property supposed to be in each individual thing that makes it an individual (i.e. a certain “thisness”). Duns Scotus also developed a complex argument for the existence of God, and argued for the Immaculate Conception of Mary. The intellectual tradition derived from Scotus' work is called Scotism.