Imagine you’re a scientist with a set of results that are equally well predicted by two different theories. Which theory do you choose?
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. 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.
Occam’s razor is often stated as an injunction not to make more assumptions than you absolutely need. 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.”