Largely because planetary orbits are in fact elliptical, not circular, he still needed them (and other tinkering, such as a slightly off-center Sun) to make the scheme work. First, Copernicus didn’t do away with epicycles. The two theories explained the same astronomical observations, but Copernicus’s was simpler, and so Occam’s razor tells us to prefer it. Then along came the Polish astronomer with his heliocentric universe, and no more epicycles were needed. It is often claimed that, by the 16th century, this Ptolemaic model of the universe had become so laden with these epicycles that it was on the point of falling apart.

These could account, for example, for the way the planets sometimes seem, from the perspective of the Earth, to be executing backwards loops along their path. In order to get the mistaken geocentric theory to work, ancient philosophers had to embellish circular planetary orbits with smaller circular motions called epicycles. Take the debate between the ancient geocentric view of the universe-in which the sun and planets move around a central Earth-and Nicolaus Copernicus’s heliocentric theory, with the Sun at the center and the Earth and other planets moving around it. Worse still, the history of science is often distorted in attempts to argue that it has. I have found no single instance where it has served this purpose to settle a scientific debate. The worst misuses, however, fixate on the idea that the razor can adjudicate between rival theories. There’s no easy equation between simplicity and truth, and Crick’s caution about Occam’s razor just perpetuates misconceptions about its meaning and value. While it’s true that “simple, elegant” theories have sometimes turned out to be wrong (a classical example being Alfred Kempe’s flawed 1879 proof of the “four-color theorem” in mathematics), it’s also true that simpler but less accurate theories can be more useful than complicated ones for clarifying the bare bones of an explanation. But it’s what Francis Crick was driving at when he warned that Occam’s razor (which he equated with advocating “simplicity and elegance”) might not be well suited to biology, where things can get very messy. There’s absolutely no reason to believe that. It is invoked in the same spirit as that attested by Newton, who went on to claim that “Nature does nothing in vain, and more is in vain, when less will serve.” Here the implication is that the simplest theory isn’t just more convenient, but gets closer to how nature really works in other words, it’s more probably the correct one. There’s no easy equation between simplicity and truth.īut Occam’s razor is often fetishized and misapplied as a guiding beacon for scientific enquiry. Applied this way, simplicity is a practical virtue, allowing a clearer view of what’s most important in a phenomenon. That’s why most scientific theories are intentional simplifications: They ignore some effects not because they don’t happen, but because they’re thought to have a negligible effect on the outcome. This sounds like good sense: Why make things more complicated than they need be? You gain nothing by complicating an explanation without some corresponding increase in its explanatory power.

Isaac Newton more or less restated Ockham’s idea as the first rule of philosophical reasoning in his great work Principia Mathematica (1687): “We are to admit no more causes of natural things, than such as are both true and sufficient to explain their appearances.” In other words, keep your theories and hypotheses as simple as they can be while still accounting for the observed facts.

What William actually wrote (in his Summa Logicae, 1323) is close enough, and has a pleasing economy of its own: “It is futile to do with more what can be done with fewer.”

Occam’s razor is often stated as an injunction not to make more assumptions than you absolutely need. Called Ockam’s razor (more commonly spelled Occam’s razor), it advises you to seek the more economical solution: In layman’s terms, the simplest explanation is usually the best one. This, it’s often said, is just where you need a hypothetical tool fashioned by the 14th-century English Franciscan friar William of Ockham, one of the most important thinkers of the Middle Ages. Imagine you’re a scientist with a set of results that are equally well predicted by two different theories.

William of ockham quote