Okham's Razor

Sharon Kaye

                                            The Royal Institute of Philosophy - Publication Date: 01/06/2003

There are so many interesting theories about the nature of reality. How do we decide which to accept and which to reject? As we go through life, we examine new ideas and reexamine old ones in an attempt to establish a suitable collection of beliefs. Sometimes this process feels like walking through the a la carte line in a cafeteria where you can pick and choose any combination you want. Just as a smart eater will use healthy principles to make these choices, a smart thinker will use epistemic principles to evaluate beliefs.

Ockham’s Razor is one of the most important epistemic principles. It states that if you have to choose from some number of competing theories, choose the simplest theory because it is most likely to be true.

Suppose, for example, that the newspaper, which is delivered daily to your doorstep, is missing this morning. There are a number of possible explanations. The delivery person could be ill, the newspaper plant may have shut down, or outer space aliens may have stolen it for the purpose of spying on Earthlings. The obvious choice among these three possibilities is the first. The second and third choices seem increasingly unacceptable. But why? If the choice is mine, what is there to prevent me from accepting the alien theory?

The answer is that the alien theory is too complicated. The illness theory requires me to believe in the presence of a virus, something I already believe in for other reasons. The alien theory, in contrast, requires me to believe in something that I have no other reason to acknowledge. This is to say that the alien theory asks me to adopt more assumptions than does the illness theory.

One might still wonder why added assumptions constitute a problem. After all, it is not as though we are short on brain space. My interest in creativity and originality might lead me to take pride in developing a more complicated theory.

But this would be a mistake. Complication is not something to take pride in because it necessarily increases the risk of error. Each and every belief is a liability insofar as it carries the possibility that it may not be true. The more assumptions you adopt, therefore, the more likely it is that you have unknowingly committed yourself to a falsehood. Falsehood is the great enemy of intelligence. To live intelligently, we must minimize the risk of error as much as we can.

Ockham’s Razor does not state that the world is maximally simple. Clearly, the world is not simple. The world is so complex that it would not be entirely surprising if it turns out that outer space aliens do exist. The point is that we should not move to that conclusion until the evidence forces us there – until we are not able to explain what we observe in a simpler way.

Philosophers have used the Razor in many different ways. Sometimes they use it to defend traditional views. The great twentieth-century philosopher Bertrand Russell appeals to the Razor in his refutation of idealism, the view that the external world does not exist. Russell writes:

Thus every principle of simplicity urges us to adopt the natural view, that there really are objects other than ourselves and our sense-data which have an existence not dependent upon our perceiving them. . . . Since this belief does not lead to any difficulties but on the contrary tends to simplify and systematize our account of our experiences, there seems no good reason for rejecting it. (The Problems of Philosophy, Oxford University Press, 1968, p. 24.)

On the other hand, philosophers have also used the Razor to attack traditional views. For example, atheists increasingly use it against theism. If we can now explain everything about the world that there is to be explained in purely natural terms, then there is no need for the supernatural assumption. Sure, you can still add it if you want, but it is no longer an intelligent choice.

As this last example suggests, there is room for disagreement over the use of Ockham’s Razor. After all, positing an extra entity can actually simplify a theory. (Imagine trying to do physics without the electron.) Richard Swinburne argues that the God hypothesis performs a similar function. Like any philosophical tool, the Razor is itself controversial, raising some interesting epistemological questions.

One question about the Razor that is rarely asked, however, is this: why is it called a Razor? When I ask my students this question, they often answer that it is called a Razor because it trims the fat. It is true that trimming the fat is an apt metaphor for what the principle of simplicity accomplishes insofar as it signifies getting to the "meat of the matter," the essentials. But who uses a razor for trimming fat? Ask any butcher and you will learn that there are plenty of other more effective tools for such a procedure.

Ockham’s Razor is named after the fourteenth-century logician, William of Ockham. Although he did not invent the principle of simplicity, he used it so effectively and with such devastating effect, that it became indelibly associated with him. Did they use razors for trimming fat back in the Middle Ages?

Of course not. The primary use for the razor in the Middle Ages was the same as it is today: shaving. The problem is that, unlike trimming fat, shaving is not an apt metaphor for what the principle of simplicity accomplishes. Setting aside certain medical contexts, shaving is a cosmetic procedure. We shave to beautify ourselves, not to simplify ourselves. In fact, one could argue that shaving makes personal hygiene considerably more complicated. Nor do we shave to get down to the essentials as though a bald man is somehow more authentic than a hirsute. Shaving is a matter of personal preference. If the epistemic principle in question were about personal preference, then it should have been named the ‘principle of prettiness’. Granted, ‘elegance’ has long been regarded as a desirable quality in theories, and elegance is closely related to simplicity. But since when is hair inelegant? Just what were they thinking when they named Ockham’s Razor?

My own personal theory is that they were thinking about another use of the razor during the Middle Ages. At the end of the fourteenth century, paper was only just being introduced in Europe as a common writing material. Before then, everything was written on parchment, which is made from animal skins. The picture below features a typical medieval scribe:

Notice the tools he holds. In his right hand is a quill for applying ink. In his left hand is a razor. He uses the razor to scrape the parchment clean when he makes an error. His razor is an eraser.

I believe that we would all do well to be more conscious of the principle of simplicity. It is not a matter of personal preference; it is a matter of accuracy. Ockham’s Razor is the way to keep your mind neat and clean.

Sharon Kaye is assistant professor in philosophy at John Carroll University Cleveland, Ohio