• Friar and Philosopher William of Ockham, 1288
  

William of Ockham joined the Franciscan order at an early age. It is believed that he studied theology at the University of Oxford from 1309 to 1321, but never completed his master's degree (the usual undergraduate degree in those times). Because of this, he acquired the byname Venerabilis Inceptor, or "Worthy Beginner" (an inceptor was a student formally admitted to the ranks of teachers by the university authorities). He was also known as the Doctor Invincibilis or "Unconquerable Teacher."

His work in this period became the subject of controversy, and many scholars have thought that Ockham was summoned before the Papal court of Avignon in 1324 under charges of heresy. During the Middle Ages of Europe, theologian Peter Lombard's Sentences (1150) had become a standard work of theology, and many ambitious theological scholars wrote commentaries on it. William of Ockham was among these scholarly commentators. However, Ockham's commentary was not well received by his colleagues, or by the church authorities. In 1324, his commentary was condemned as unorthodox by a synod of bishops, and he was ordered to Avignon, France, to defend himself before a papal court. For two years, he was confined to a Franciscan house, until he was condemned as a heretic in 1326.

An alternative theory, recently proposed by George Knysh, suggests that he was initially appointed in Avignon as a professor of philosophy in the Franciscan school, and that his disciplinary difficulties did not begin until 1327. It is generally believed that these charges were levied by Oxford chancellor John Lutterell. It was in this year that the Franciscan Minister General, Michael of Cesena, had been summoned to Avignon, to answer charges of heresy. A theological commission had been asked to review his Commentary on the Sentences, and it was during this that Ockham found himself involved in a different debate. Michael of Cesena had asked Ockham to review arguments surrounding Apostolic poverty. (The most uncompromising Franciscans, known as spirituals, believed that Jesus and his apostles owned no personal property, and survived by begging and accepting the gifts of others). This brought them into conflict with Pope John XXII.

Eventually, fearing imprisonment and possible execution, Ockham, Michael of Cesena and other Franciscan sympathizers fled Avignon on 26 May 1328, and eventually took refuge in the court of the Holy Roman Emperor Louis IV of Bavaria - who was also engaged in dispute with the papacy, and became Ockham's patron. After studying the works of John XXII and previous papal statements, Ockham agreed with the Minister General. In return for protection and patronage Ockham wrote treaties that argued for King Louis to have supreme control over church and state in the Holy Roman Empire. For doing this Ockham was solemnly excommunicated by Pope John XXII, while Ockham believed that John XXII was himself guilty of heresy for refusing to accept the Franciscan claim. However, though Ockham was excommunicated, his philosophy was never officially condemned.

He spent much of the remainder of his life writing about political issues, including the relative authority and rights of the spiritual and temporal powers. After Michael of Cesena's death in 1342, William became the leader of the small band of Franciscan dissidents living in exile with Louis IV. Ockham died (prior to the outbreak of the plague, or Black Death) either on 10 April 1347 or (more likely) on 9 April 1348 in the Franciscan convent at Munich in Bavaria. He was officially rehabilitated by Innocent VI in 1359.

William of Ockham believed "only faith gives us access to theological truths. The ways of God are not open to reason, for God has freely chosen to create a world and establish a way of salvation within it apart from any necessary laws that human logic or rationality can uncover." Ockham's theism was based solely on private revelation and faith (he supported some sort of Non - overlapping magisteria). He believed that only science was a matter of discovery and saw God as the only ontological necessity.

In scholasticism, Ockham advocated a reform both in method and in content, the aim of which was simplification. Ockham incorporated much of the work of some previous theologians, especially John Duns Scotus. From Scotus, Ockham derived his view of divine omnipotence, his view of grace and justification, much of his epistemology and ethical convictions. However, he also reacted to and against Scotus in the areas of predestination, penance, his understanding of universals, his distinction ex parte rei (that is, "as applied to created things"), and his view of parsimony.

A pioneer of nominalism, some consider him the father of modern epistemology, because of his strongly argued position that only individuals exist, rather than supra - individual universals, essences, or forms, and that universals are the products of abstraction from individuals by the human mind and have no extra - mental existence. He denied the real existence of metaphysical universals and advocated the reduction of ontology. Ockham is sometimes considered an advocate of conceptualism rather than nominalism, for whereas nominalists held that universals were merely names, i.e., words rather than existing realities, conceptualists held that they were mental concepts, i.e., the names were names of concepts, which do exist, although only in the mind. Therefore, the universal concept has for its object, not a reality existing in the world outside us, but an internal representation which is a product of the understanding itself and which "supposes" in the mind the things to which the mind attributes it; that is, it holds, for the time being, the place of the things which it represents. It is the term of the reflective act of the mind. Hence the universal is not a mere word, as Roscelin taught, nor a sermo, as Abelard held, namely the word as used in the sentence, but the mental substitute for real things, and the term of the reflective process. For this reason Ockham has been called a "terminist", to distinguish him from a nominalist or a conceptualist.

One important contribution that he made to modern science and modern intellectual culture was the principle of parsimony in explanation and theory building that came to be known as Occam's Razor. This maxim, as interpreted by Bertrand Russell, states that if one can explain a phenomenon without assuming this or that hypothetical entity, there is no ground for assuming it, i.e., that one should always opt for an explanation in terms of the fewest possible causes, factors, or variables. He turned this into a concern for ontological parsimony; the principle says that one should not multiply entities beyond necessity – Entia non sunt multiplicanda sine necessitate – although this well known formulation of the principle is not to be found in any of Ockham's extant writings. He formulates it as: "For nothing ought to be posited without a reason given, unless it is self evident (literally, known through itself) or known by experience or proved by the authority of Sacred Scripture." For Ockham, the only truly necessary entity is God; everything else is contingent. He thus does not accept the principle of sufficient reason, rejects the distinction between essence and existence, and advocates against the Thomistic doctrine of active and passive intellect. His skepticism to which his ontological parsimony request leads appears in his doctrine that human reason can prove neither the immortality of the soul nor the existence, unity, and infinity of God. These truths, he teaches, are known to us by Revelation alone.

Ockham wrote a great deal on natural philosophy, including a long commentary on Aristotle's physics. According to the principle of ontological parsimony, he holds that we do not need to allow entities in all ten of Aristotle's categories; we thus do not need the category of quantity, as the mathematical entities are not "real". Mathematics must be applied to other categories, such as the categories of substance or qualities, thus anticipating modern scientific renaissance while violating Aristotelian prohibition of metabasis.

In the theory of knowledge, Ockham rejected the scholastic theory of species, as unnecessary and not supported by experience, in favor of a theory of abstraction. This was an important development in late medieval epistemology. He also distinguished between intuitive and abstract cognition; intuitive cognition depends on the existence or non existence of the object, whereas abstractive cognition "abstracts" the object from the existence predicate. It is not yet decided among interpreters as to the role of these two types of cognitive activities.

Ockham is also increasingly being recognized as an important contributor to the development of Western constitutional ideas, especially those of government with limited responsibility. He was one of the first medieval authors to advocate a form of church / state separation, and was important for the early development of the notion of property rights. His political ideas are regarded as "natural" or "secular", holding for a secular absolutism. The views on monarchical accountability espoused in his Dialogus (written between 1332 and 1348) greatly influenced the Conciliar movement and assisted in the emergence of liberal democratic ideologies.

In logic, Ockham wrote down in words the formulae that would later be called De Morgan's Laws, and he pondered ternary logic, that is, a logical system with three truth values; a concept that would be taken up again in the mathematical logic of the 19th and 20th centuries.

Ockham and his works have been discussed as a possible influence on several late medieval literary figures and works, especially Geoffrey Chaucer, but also Jean Molinet, the Gawain Poet, François Rabelais, John Skelton, Julian of Norwich, the York and Townely Plays, and Renaissance romances. Only in very few of these cases is it possible to demonstrate direct links to Ockham or his texts. However, correspondences between Ockhamist and Nominalist philosophy / theology and literary texts from medieval to postmodern times have been discussed within the scholarly paradigm of literary nominalism.