William of Ockham

William of Ockham (c. 1287-1347) was an English Franciscan friar, philosopher, logician and theologian, and one of the central figures of fourteenth-century scholastic thought. He was the most prominent representative of nominalism against the Thomist and Scotist schools. He is best known for Occam's razor, a principle of explanatory economy that bears his name and is still invoked in discussions of scientific theory.

He was probably born in Ockham, Surrey, and joined the Franciscan Order while still very young, receiving his early education in the Franciscan houses in London and Oxford. He never completed the requirements to become a regent master, which is why he was known as Venerabilis Inceptor. Most of his logical, physical and theological writings date from these years. He later taught in Paris, where Jean Buridan was among his students.

In 1324 he was summoned to Avignon to answer for his commentary on Peter Lombard's Sentences. The case dragged on without a formal verdict. There he became entangled in the dispute over apostolic poverty. In May 1328 he left the city with Michael of Cesena and other friars, took refuge in Munich under the protection of Emperor Louis IV of Bavaria, and was excommunicated. From then on he wrote mainly on the powers of the temporal and spiritual authorities, and came to argue that Pope John XXII was a heretic. He died in Munich in 1347, probably of the Black Death. The Church rehabilitated him posthumously in 1359.

His philosophy aimed to simplify both the method and the content of scholasticism. From Duns Scotus he took his account of divine omnipotence and much of his epistemology and ethics, but he parted ways with him on questions such as universals. For Ockham, universals are not independent real things but terms: words, signs or concepts that stand for similar individuals. Only God is necessary; everything else is contingent. Human reason, he held, cannot by itself prove God's existence, unity and infinity, or the immortality of the soul. These truths are known through revelation alone. He also held that theology is not a science in the strict sense, and he rejected the theory of intelligible species in favour of an account based on abstraction.

His influence proved lasting. Fifteenth-century nominalists regarded him as one of their founders. He is often linked to modern science, English empiricism and analytic philosophy because of his insistence on clear reasoning and on not multiplying assumptions. His political writings also fed debates about the limits of papal authority.