If you’ve ever spent any time arguing on the internet, you’ve likely come across a philosophical principle known as ‘Ockham’s Razor.’ Along with ad hominem attacks and comparing people you don’t like to Hitler, Ockham’s Razor is a favourite argument of keyboard warriors everywhere, most often understood as meaning “the simplest argument is most often the correct one.” But where did this strangely-named principle come from, and does it hold as much rhetorical weight as many seem to think it does? Or is it just something people use in order to sound smarter and win arguments?

To begin with a brief back story. Ockham’s Razor is named after Willam of Ockham, an English Franciscan friar and theologian who lived during the 13th and 14th Centuries. Born in the town of Ockham in Surrey in 1258, little is known about Ockham’s early life prior to his joining the Franciscan Order at age 14. As we shall soon see, his choice of monastic order would have a profound impact on his philosophical views and the theological controversies in which he would later become embroiled. Ockham began his education at the London Convent for the Franciscan Order, studying the usual scholastic topics such as logic, natural philosophy, and theology. From 1310 to 1317 he studied theology at Oxford University and began lecturing on bishop Peter of Lombard’s Four Books of Sentences, the standard handbook for theologians at the time.

It was Ockham’s lectures and commentary on the Sentences which first landed him in hot water with the Catholic Church on philosophical and theological grounds. As a Franciscan, Ockham was theologically at odds with the dominant Dominican Order, whose views at the time were epitomized by the writings of Saint Thomas Aquinas. Among the many issues over which the Franciscans and Dominicans disagreed was whether Jesus and his followers owned property. Saint Francis of Assisi, the founder of the Franciscan Order, had concluded that Jesus did not own property and modelled his own monastic order on his example, requiring his monks to take a vow of poverty and rely on the charity of others for food, shelter, and other necessities. He even went so far as to tear down a brand-new home specially built for his Order. Ockham passionately upheld these views, and in 1324 a rival at Oxford reported him to Pope John XXII, who summoned Ockham to the Papal Court – at that time based in Avignon, France – for a hearing. Ockham saw the Catholic Church’s vast accumulation of wealth and power as antithetical to Jesus’s teachings and even went so far as to declare the Pope a heretic and call for his abdication. For the next four years Ockham lived in Avignon as the hearings dragged on and the conflict between the Dominicans and Franciscans grew ever more heated, until finally making his escape in 1328. He travelled around Italy and Germany for a while before settling in Munich, where he lived out the rest of his life before dying in 1347.

Much of Ockham’s philosophical career was devoted to metaphysics and logic, and it is from this work that we get his famous Razor. The school of Medieval philosophy in which Ockham worked, also known as Scholasticism, was quite different from our modern conceptions of philosophy and logic, being heavily centred on theology and the writings of Aristotle. The focus on theology in particular can make Scholasticism seem very alien to modern philosophy students and has given the discipline something of a bad reputation. The reality, however, is rather more complicated, and the work of William of Ockham serves as a good case study for how Scholasticism helped lay the groundwork for modern-day Empiricism and Analytical Philosophy.

Much of Ockham’s scholarship dealt with the problem of Universals, entities which exist in relation to other entities and which unite similar entities as general properties. For example, according to this framework, chairs owe their existence to the property of “chairness,” which informs what in the physical world can and cannot be a chair. Competing schools of philosophy differ on whether Universals are independent of the objects they signify, or a fundamental property of the objects themselves. Ockham, as a Nominalist, did not believe that Universals actually existed. For him, a chair was just a chair – not part of a universal metaphysical property but rather simply a mental concept used to describe a group of related objects. Although a chair shares features with other individual chairs, the similarities are in the mind of the observer, not a fundamental property of the physical world. While all this may seem like esoteric navel-gazing, Ockham’s rejection of the more metaphysically extraneous aspects of older Aristotelian philosophy – including the concept of Universals – led to the development of a simpler, more stripped-down metaphysical worldview that would later evolve into Empiricism and the Scientific Method. It also directly informed the principle known today as “Ockham’s Razor.”

Ockham’s Razor is typically stated as “Entities should not be multiplied beyond necessity.” In other words, when comparing two arguments, all other things being equal, the simplest explanation is most likely to be the correct one. While this principle is today widely associated with William of Ockham, Ockham himself never stated his famous Razor in its modern form in any of his known writings. Indeed, the basic idea of Ockham’s Razor, known as the principle of parsimony, actually predates Ockham by centuries, first appearing in the works of Aristotle:

“Nature does nothing in vain, but always does what is best from among the possibilities, for the substantial being of each kind of animal.”

The principle of parsimony also appears in the works of dozens of Hellenic, Jewish, Muslim, and Christian European philosophers prior to the Fourteenth Century. So why is it most commonly associated with William of Ockham? The most commonly held theory is that the principle was attributed to him by later scholars like theologian and astronomer Libert Froidmont’s, who in his 1649 book On Christian Philosophy of the Soul wrote:

“I call this axiom Ockham’s and the Nominalists’ razor because they used [it] to trim and shave off all distinct entities, leaving a plurality only of names.”

Whatever its origin or specific historical formulation, the basic principle of Ockham’s razor remains the same: as theories are intended to explain natural phenomena, the fewer assumptions and convolutions a theory has, the stronger it is likely to be – or, as doctors are often advised when making diagnoses: when you hear hoofbeats, think horses, not zebras. This principle became especially important as Western philosophy moved into the Enlightenment and old ideas about the universe began to be challenged. For example, for thousands of years philosophers believed that the Earth was at the centre of the universe and that the cosmos revolved around it. However, this theory was fundamentally flawed, for certain celestial objects, known as planets, appeared to periodically stop in their tracks and reverse direction, a phenomenon known as retrograde motion. Indeed, the word “planet” is derived from the Greek word planetai, meaning “wanderers.” In order to resolve this apparent contradiction, in the 3rd and 2nd Centuries B.C.E. Greek philosophers Hipparchus and Ptolemy devised a model of the universe in which the planets not only revolved around the earth but also around smaller orbits known as “epicycles,” the combination of which accounted neatly for retrograde motion. However, as astronomers discovered ever  more apparently contradictory celestial phenomena, the Ptolemaic model grew into a cumbersome, convoluted mess of “circles within circles.” By contrast, the Geocentric model championed by Nicolaus Copernicus and Galileo Galilei, which placed the sun and not the earth at the centre of the universe, provided a far more elegant explanation for retrograde motion. According to this model, the phenomenon was the result of planets orbiting the sun at different speeds, causing certain planets to periodically overtake each other and create the illusion of reversing motion. In the absence of other evidence, the Copernican model was eventually accepted as more likely to be accurate as it explained the same natural phenomena with fewer assumptions and convolutions.

But while Ockham’s Razor is a useful tool when comparing competing theories, it is not the end-all-be-all rule it is so often made out to be. After all, the simplest explanation is not always the correct one – especially in science. For example, Aristotle believed that all objects have a natural tendency to fall towards the centre of the universe. As the Earth was believed to be at the centre of the universe, this philosophy neatly explained the phenomenon of gravity. Later, however, Isaac Newton demonstrated that gravity is, in fact, an attractive force produced by all objects with mass; while later still Albert Einstein revealed that gravity is the result of the mass of objects distorting the fabric of spacetime. In each case the explanation for the force of gravity grew ever more complicated, while simultaneously allowing natural phenomena to be modelled and predicted to an ever-increasing degree of accuracy. Indeed, the simplicity of a scientific theory has little bearing on the likelihood of it being true; all that matters is whether said theory can accurately predict the outcome of an experiment. This demonstrates the vital importance of the caveat “all things being equal” in the traditional formulation of Ockham’s Razor. In the vast majority of cases, competing theories do not stand on equal ground; one will always have a larger body of empirical evidence backing it up, rendering the application of Ockham’s Razor moot.

However, Ockham’s Razor does have its applications in science, particularly in relation to a principle known as falsifiability. First introduced by Austrian philosopher Karl Popper in his 1935 work The Logic of Scientific Discovery, the falsifiability principle was inspired by what Popper saw as a fundamental difference between the physical sciences and other scientific fields – specifically, between Einstein’s theories of Relativity and Freud’s theories of Psychoanalysis. Popper instinctively viewed the former as inherently more scientific than that latter, but initially could not articulate exactly why. He later realized that the difference lay in the ability of each theory to be disproven through experimental evidence. Psychoanalytic theory, he observed, was incapable of being disproven; if an observed behaviour was found to contradict one of Freud’s theories, then another was immediately offered up to explain the discrepancy – a practice known in science as an ad hoc hypothesis. Even though it was impossible for every theory to be correct at the same time, there was no mechanism to determine which theory was, in fact, the correct one. Einstein’s theories, by contrast, were inherently “riskier” in that it was possible to disprove them through experiment. For example, General Relativity predicted that the gravity of the sun would deflect the light of distant stars by a certain amount – an amount which differed from that predicted by Newtonian mechanics. Thus, if this deflection were to be measured – as it was by physicist Arthur Eddington in 1919 – there would be two possible outcomes: one which supported Einstein’s theories and one which falsified it. The upshot of all this is that, counter-intuitively, a theory which explains everything and cannot be disproven is, in fact, an inherently weak theory and belongs in the realm of pseudoscience. Thus, applying a form of Ockham’s Razor, a strong theory is one which includes the smallest number of assumptions and ad hoc hypotheses and is fundamentally testable and -most importantly – falsifiable.

On a more basic level, many philosophers have argued that the over-use of Ockham’s Razor can stifle creativity and lead to overly narrow-minded thinking. Walter Chatton, a contemporary of William of Ockham, even put forward his own “anti-razor”, also known as the principle of plenitude:

“Wherever an affirmative proposition is apt to be verified of actually existing things, if two things… are not able to suffice without another thing, one has to posit another thing.”

Similarly, German philosopher Immanuel Kant stated:

“The variety of entities should not be rashly diminished”

Surprisingly, the Razor and Anti-Razor do not actually contradict each other but rather act as safeguards against extremes in thought when formulating theories, with the Razor opposing the unnecessary addition of complexity and the Anti-Razor opposing the unnecessary elimination of complexity. In philosophy and science, as in all things, moderation, rationality, and careful thought are the key to uncovering the truth.

Thus, Ockham’s Razor is much like its physical counterpart: you can get a nice close shave, just be careful you don’t cut too close.

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