William of Ockham
English Franciscan friar, philosopher and scholastic theologian (c. 1287–1347), probably born in the village of Ockham, in Surrey, and educated at Oxford, where he taught theology without ever formally obtaining the master's chair, owing to a heresy charge that led him to appear before the papal court at Avignon, where he remained under investigation for nearly four years without ever being formally condemned. A central figure of late scholasticism and regarded as the foremost exponent of medieval nominalism, Ockham developed a radical critique of the dominant Platonic and Aristotelian realism, arguing that universals — general concepts such as 'humanity' or 'whiteness' — have no independent real existence, either in the divine mind or in the world, but are merely names (nomina) or mental constructs we use to refer to similarities among individual things, the latter being the only entities that actually exist. This nominalist position underlies the methodological principle for which he is universally known, 'Ockham's razor', formulated in various ways across his work but traditionally summarised as 'entities must not be multiplied beyond necessity' (entia non sunt multiplicanda praeter necessitatem): faced with rival explanations of a phenomenon, one should always prefer the simplest, the one positing the fewest entities or assumptions, a principle that, though not originally his own invention, he applied so systematically that it became indelibly associated with his name, and which remains today a basic methodological principle of science and philosophy. Ockham also firmly defended a strict separation between faith and reason, arguing that fundamental theological truths — such as the existence of God or the immortality of the soul — could not be demonstrated by natural reason but only accepted by faith, a position that, by weakening the rationalist claims of natural theology, paradoxically helped free philosophical and scientific inquiry from theological constraints. Also involved in the political debates of his time concerning the relationship between papal and secular power, advocating a limitation of papal authority, he probably died of the Black Death in Munich, where he had taken refuge under the protection of Emperor Louis of Bavaria after being excommunicated by the pope.