OCCAM'S DISPOSABLE RAZOR

5 Oct 1996
Source: The Economist
OCCAM'S DISPOSABLE RAZOR
Is Seeing Believing?

The Roswell tape--the film, released last year, of an autopsy on a purported alien who had met an unfortunate end by crashing into New Mexico--earned many journalists their keep for another week. Several tried to reassure readers that aliens could not exist, because their doing so would offend the principle of economy known as Occam's razor: "Entities should not be multiplied unnecessarily."

One employed ridicule. "Occam's razor has it that you should not multiply entities...but UFO freaks like nothing better than to multiply entities, particularly those with six fingers and weird eyes." Another launched a mixed-metaphor attack: "The old saw (Occam's razor)...slices up the little green men better than [the] autopsy." Months later, a book reviewer complained: "Six hundred years after William of Occam cut the ribbon on the age of science...between a third and two-thirds of the population still believes in paranormal superfluities such as telepathy, precognition and reincarnation."

Occam's principle did say that superfluous things should not exist; but it was devised only to cut through the metaphysical mess that the philosophy of his time was producing. Since then, however, flabby thinkers have manufactured from it a sort of philosophical spot cream, the liberal application of which makes undesirable things vanish. Worse, it gets used to prop up all manner of otherwise unsupported notions. It has stood in for management non-ideas: "Applying Occam's razor, a [business] unit should be as small as it can be and as large as it must be to survive"--or even to make simple questions look deep: "Applying the scientific principle of Occam's razor..what was so special about PanAm flight 103?"

Occam here, Occam there, Occam, Occam everywhere--like the barber of Seville, the barber of philosophy has been hoisted by his own popularity. People credit him for their own bad ideas and blame him for other people's. And all over something that he did not, in fact, really invent.

The principle of economy is traced by philosophers back to Aristotle. For the scholastic philosophy of Occam's time, Aristotle was virtually the reference point--though a confused one, thanks to a dozen centuries of dilution and retranslation.

Long before Occam, the principle was used for excising unnecessary entities from the theory of perception. For an object--a bottle, say--to be perceived, a representation of it has to get through from the object to the mind of the perceiver. In Occam's day, most argued that it made the journey as a series of "species"--strange entities running a sort of relay race, through the external medium, then the external sense organs, to the internal ones, ending in an image of the object. Debates raged about which species existed, with each philosopher criticising another's use of the principle of economy.

The common wisdom is that Occam went further, and rejected the existence of "universals." Until then, it had been thought that recognising a bottle as a bottle meant connecting the image of it with some abstract idea of bottleness. This idea--the universal--also had to exist in the mind. By denying that it did, Occam supposedly laid the ground for modern science, which believes in specific bottles, not a universal one.

However, according to a minority view (shared by Bertrand Russell), Occam was posthumously squeezed into this role, by historians needing to explain how western thought passed from superstition to science. Occam did not deny universals, say the dissidents; he aimed to restore the real Aristotle by getting rid of the accreted misconceptions about him. In doing so he criticised every standard reading of Aristotle, including the interpretation of universals, and was thus unwittingly hailed as the father of modern scientific method.

Indignity enough. Worse still, scientific method wants no part of it. The belief that Occam's razor is a scientific principle stems from a subtle confusion between parsimony (the denial of unnecessary entities--ie, Occam's razor) and simplicity.

Scientists like simple theories. If two theories agree equally well with experiment, the simpler one usually gets chosen, just because it is easier to use. It makes sense to do things simply, like walking in a straight line rather than a wobbly line.

Parsimony--ie, not believing in unseen entities, be they tiny particles, intelligent life on other planets or God--is merely a philosophical principle, not a scientific one. (You cannot have scientific evidence that aliens do not exist if you have never seen an alien). There is no logical reason why a parsimonious theory, rather than an extravagant one, should be true. Yet, since it describes the same observations with less fancy detail, it is likely to be simpler too; so scientists are likely to choose it.

The scientists are often vindicated. Take the solar system. In challenging the geocentric model that had the planets dancing a complex set of epicycles to explain their erratic motions as seen from the earth, Copernicus found that the same thing would be seen if the planets, and the earth, went round the sun. His theory was both simpler and more parsimonious.

This and many other examples have led many scientists to associate simplicity and parsimony not only with ease, but with truth. On the face of it, this looks fine: surely it is wise to go for the simpler explanation and reject things you have no positive evidence for, like epicycles or aliens or God? Well, no. It merely seems to be, because things have been simple in the past.

What this implies is that the universe is somehow inherently simple--an idea that gives ulcers to some philosophers and pay packets to all. Some argue that the history of science shows no such trend, and that Occam's razor, indeed, has conditioned people to see simplicity where there is none.

Most scientists carry on in blissful disregard. They see pragmatic reasons why simple theories might win out. This is a universe in which all things are made up of progressively smaller, simpler ones. As a science advances, it usually generalises, covering more phenomena. To do so it must theorise about what they have in common, and, in this universe, that is something more basic. So newer, broader theories describe increasingly basic things;(and also have fewer exceptions), hence are simpler themselves. Of course, the things they describe (like electrons) are far from everyday experience, so the theories seem hideously complex to all but their cognoscenti.

Either way, Occam loses. His razor was made for the philosophical realm, but gets dragged into the real world as some kind of mystical truth to explain the universe. The explanation turns out to be either flawed or unnecessary, and he gets the blame for confusing people. His other, very advanced, philosophical and political ideas have been overshadowed. And to crown it, foolish people turn his razor into an amulet, and use it to ward off little green men.

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