Occam's Razor: to cut or not to cut?

On the elegance - and the temptations - of simple explanations

All things being equal, the simplest solution is usually the best one.
William of Ockham

You’ve probably heard the old adage that if you hear the pounding of hooves echoing through the Wiltshire countryside you shouldn’t assume a herd of zebras is on its way. The simplest explanation for a phenomenon is the likeliest and in this case you’re probably safer to expect to see some horseflesh any moment. Of course, this isn’t always the case. If you’re on the African savannah then zebras are a more reasonable expectation. There are, of course, times when the simplest explanation won’t turn out to be true, but it’s a sensible starting point for investigation.

This simple rule of thumb, has been widely attributed to the 14th-century English logician and philosopher, William of Ockham (or Occam), but actually it’s been around a lot longer than that. Aristotle first suggested the idea that perfection equals simplicity: “The more perfect a nature is, the fewer means it requires for its operation.” Its Latin name is lex parsimoniae, the law of parsimony, exemplified in the maxim, ‘It is pointless to do with more what is done with less’. This is pretty straightforward and tells us to avoid concocting fanciful theories if a simple one will suffice.

Daniel Dennett gives this example:

If exposure to extremely cold air can account for all the symptoms of frostbite, don’t postulate unobserved “snow germs” or “Arctic microbes”. Kepler’s laws explain the orbits of the planets; we have no need to hypothesise pilots guiding the planets from control panels hidden under the surface.

So far so good. Occam’s razor is the principle on which the scientific method is built. For instance, the physicists Hendrik Lorentz and Albert Einstein both concluded independently that the closer we get to moving at the speed of light, the more we slow down. But while both arrived at the same results from their equations, Lorentz’s explanation relied on changes that take place in the ‘the ether’. Because Einstein made no reference to a non-existent , mystical substance, his explanation was accepted as the most likely.

Unfortunately, though, simplicity is not always as simple as it seems. Just because an explanation is easy to come by doesn’t make it either simple or sensible. For example, in education, it’s common for teachers to assume an intervention is effective simply because students seem engaged or productive. But does that really mean the intervention is working?

I’ve previously explained that performance (what we can do in the here and now) is distinct from learning (what we might be able to do elsewhere and later) and that as a consequence, learning is functionally invisible. Just because students are completing work and appearing interested (performing) it doesn’t necessarily translate into into being able to apply this performance to new contexts (learning.) It might be tempting to think so, but how can we be sure?

Consider the common mistake of seeing improved results and attributing them directly to our actions. It’s easy to jump to the conclusion that our intervention caused the change, but correlation is not the same as causation. Results can fluctuate naturally: just look at research from Ofqual on ‘natural volatility,’ which shows that year-on-year exam results can change by as much as 10-19%. It’s tempting to claim credit when things go well and shift blame when they don’t, but it’s worth asking: How much of this really has to do with our actions, and how much of it is just part of the natural ebb and flow?

Here’s where Occam’s Razor comes into play. While it’s a helpful heuristic - the idea that the simpler explanation is usually the best - it doesn’t prove anything. It’s not a hard-and-fast rule but rather a guide. When faced with competing explanations, the simplest one is likely the most accurate, but we must be cautious.

It’s easy to assume that the simplest explanation is always the best, but in reality, complexity often reveals deeper insights. The allure of simplicity can make us overlook the nuanced layers that truly explain a situation. For example, just because an intervention seems to make a difference today doesn’t mean it’s the reason behind long-term success. It’s tempting to think that a quick fix will solve a problem, but the real answer often lies in a web of factors that can take time to unfold. Occam’s Razor is great for deciding between competing ideas, but it’s not always the right tool for disproving something more complex. The simplest explanation might be right, but it could also be an oversimplification.

Consider a company that launches a new product and immediately sees a rise in sales. The company might attribute the sales spike to a clever ad campaign. While the ad likely played a role, a closer look might reveal that the real driver was something less obvious, perhaps timing during a specific season, or even external factors like a shift in consumer interest or trends that were already building. If the company assumes the ad campaign alone is responsible, they might overlook important lessons about broader market shifts and miss out on ways to sustain success.

Similarly, a school implements an intervention, such as additional revision sessions for Year 11 students. At the end of the term, results appear to improve. It’s tempting to attribute the improvement solely to the intervention itself. However, a more nuanced analysis may reveal that the students were already on an upward trajectory due to external factors, such as improved student wellbeing or changes in teaching staff. Who knows? The likelihood that improvements in exam results are attributable to a single cause is naive. The improvement might not be directly due to the intervention, but instead to a complex mix of factors, all of which should be considered to understand the bigger picture.

In both cases, the simplest explanation - whether it’s the intervention, the marketing strategy, or any immediate change - often fails to account for the complexity of the situation. Sometimes, the real truth requires a deeper look into multiple interconnected factors, something Occam’s Razor may not always be equipped to unravel. Simple answers are useful, but in the real world, they often need to be tempered with more careful thought and analysis.

Correlation ≠ causation