More than any other element of his philosophy, William of Ockham (c. 1280-c. 1349) is known for “Ockham's razor,” or the principle of parsimony: “Entities are not to be multiplied beyond necessity.” The principle reflects the idea that if you possess two different theories explaining some scientific data, you should choose the one that puts forward the minimum number of entities. Ockham, like Abelard, is also known for his nonrealist theory of universals.

An English Franciscan, Ockham was dubbed the “more than subtle doctor.” He was excommunicated for his defiant defense of Franciscan poverty against Pope John XXII. He fled to Munich after being called to defend his views in front of a papal commission at Avignon in 1324. He spent the rest of his career under the protection of Emperor Louis IV of Bavaria, and promoted a separation of church and state in which the authority of neither is subordinate to the other. He died in 1347, probably from the Black Death that was raging in Munich at around that time. At the time of his death he was still hoping for reconciliation with the church.

Ockham's Razor

The reason Ockham's theory is known as the “razor” is that he cuts away unnecessary entities. It is hard to justify why a simpler explanation is preferable to a complex one, but his “razor” retains great intuitive appeal. It encourages people to cut out unnecessary complexity in favor of simplicity. Why would I assume two causes of something when one is sufficient? “It is vain to do with more what can be done with fewer,” Ockham said. Ockham's principle of parsimony is adhered to in scientific thinking today.

Ockham's Position on Universals

One example of Ockham's razor at work is his theory on universals. According to Ockham, universals like “man” and “redness” exist only in our minds. In reality, everything is singular. There are only real particulars like “this red ball” or “this man,” but beyond such singular entities there are no really existing universals. Therefore, when your mind picks out some feature like “yellowness” and “fuzzness” when you look at a tennis ball, all that you know as existing is the yellow and fuzziness of this tennis ball. You cannot say that yellowness and fuzziness exist independently of yellow and fuzzy things. Thus, Ockham, like Abelard before him, does not attribute real existence to universals and is thus opposed to Plato's theory of a realm of ideas in which abstract, universal forms exist. But Ockham is sometimes referred to as an advocate of conceptualism rather than nominalism, for nominalists contended that universals were merely names; that is, words rather than existing realities. Conceptualists held that universals were mental concepts that do exist, although only in the mind.