William of OckhamThe Razor
Ockham’s razor is the principle of parsimony or simplicity according to which the simpler theory is more likely to be true. Ockham did not invent this principle; it is found in Aristotle, Aquinas, and other philosophers Ockham read. Nor did he call the principle a “razor.” In fact, the first known use of the term “Occam’s razor” occurs in 1852 in the work of the British mathematician William Rowan Hamilton.
Although Ockham never even makes an argument for the validity of the principle, he uses it in many striking ways, and this is how it became associated with him. For some, the principle of simplicity implies that the world is maximally simple. Aquinas, for example, argues that nature does not employ two instruments where one suffices. This interpretation of the principle is also suggested by its most popular formulation: “Entities should not be multiplied beyond necessity.” Yet this is a problematic assertion.
We know today that nature is often redundant in both form and function. Although medieval philosophers were largely ignorant of evolutionary biology, they did affirm the existence of an omnipotent God, which is alone enough to render the assumption that the world is maximally simple suspicious. In any case, Ockham never makes this assumption and he does not use the popular formulation of the principle.
For Ockham, the principle of simplicity limits the multiplication of hypotheses not necessarily entities. Favouring the formulation “It is useless to do with more what can be done with less,” Ockham implies that theories are meant to do things, namely, explain and predict, and these things can be accomplished more effectively with fewer assumptions.
At one level, this is just common sense. Suppose your car suddenly stops running and your fuel gauge indicates an empty gas tank. It would be silly to hypothesize both that you are out of gas and that you are out of oil. You need only one hypothesis to explain what has happened.Some would object that the principle of simplicity cannot guarantee truth. The gas gauge on your car may be broken or the empty gas tank may be just one of several things wrong with the car. In response to this objection, one might point out that the principle of simplicity does not tell us which theory is true but only which theory is more likely to be true. Moreover, if there is some other sign of damage, such as a blinking oil gage, then there is a further fact to explain, warranting an additional hypothesis.
Although the razor seems like common sense in everyday situations, when used in science, it can have surprising and powerful effects. For example, in his classic exposition of theoretical physics, A Brief History of Time, Stephen Hawking attributes the discovery of quantum mechanics to Ockham’s razor.
Nevertheless, not everyone approves of the razor. Ockham’s contemporary and fellow Franciscan Walter Chatton proposed an “anti-razor” in opposition to Ockham. He declares that if three things are not enough to verify an affirmative proposition about things, a fourth must be added, and so on. Others call Ockham’s razor a “principle of stinginess,” accusing it of quashing creativity and imagination. Still others complain that there is no objective way to determine which of two theories is simpler. Often a theory that is simpler in one way is more complicated in another way. All of these concerns and others make Ockham’s razor controversial.
At bottom, Ockham advocates simplicity in order to reduce the risk of error. Every hypothesis carries the possibility that it may be wrong. The more hypotheses you accept, the more you increase your risk. Ockham strove to avoid error at all times, even if it meant abandoning well-loved, traditional beliefs. This approach helped to earn him his reputation as destroyer of the medieval synthesis of faith and reason.
So when we look at the world with a modern days sceptical viewpoint, we must ask, is there a simpler hypothesis? When people maintain a belief they have seen a ghost it is right to apply Ockham's razor and ask, 'Is there a simpler explanation?'