Ever heard of Occam’s razor?

It’s the principle that says the simplest explanation that fits the facts is most likely the correct one. It’s formally stated as “entities should not be multiplied without necessity.” Or informally as “keep it simple, stupid.”

Occam’s razor is named after William of Occam (sometimes spelled Ockham), an English scholar and Franciscan friar who lived from around 1288 to 1347.

Occam’s razor is so familiar to us these days that it’s almost a cliché. It’s deeply embedded in science and mathematics. Here’s Albert Einstein’s version:

“The grand aim of all science [is] to cover the greatest number of empirical facts by logical deduction from the smallest possible number of hypotheses or axioms.” [p. 7]

Yet back in the early 1300’s when William of Occam first articulated his razor, the idea was so controversial that he was summoned by the Pope in 1324 to answer charges of heresy.

Life Is Simple: How Occam’s Razor Set Science Free and Shapes the Universe takes a deep look into the origins of Occam’s razor and the influence it’s had on the world over the last 700 years. It’s written by Johnjoe McFadden, a professor of molecular genetics at the University of Surrey. Surrey, by the way, is the English county where the village of Ockham is located.

Life Is Simple:
How Occam’s Razor Set Science Free and Shapes the Universe
By Johnjoe McFadden
Basic Books, New York, 2021

Life Is Simple is mainly a history of science seen through the lens of Occam’s razor. It traces the development of science from the Medieval period up to modern times. Along the way it shows how the drive for simplicity has shaved away unnecessary assumptions, forces, entities and deities from science, philosophy, and even our general approach to problem-solving.

The book covers a lot of ground. So I’m just going to highlight a few of the themes I found most interesting.

Heresy? Seriously?

It’s hard for us to understand today why Occam’s razor was so controversial, let alone heretical, back in the fourteenth century. That’s mainly because people in Medieval Europe thought about religion, science, and the physical world so differently than we do. I think McFadden does a great job in the early chapters of the book explaining the differences. 

What we call science was actually a branch of theology in William’s day. Investigations into astronomy, geometry and other fields of science would have been understood as the study of God’s handiwork. God was the ultimate cause and the prime mover of everything that ever had or would happen. Theology was “Queen of the Sciences.” The schism of science from theology had not yet occurred.

With science subordinate to theology, you can see that any scientific idea that contradicted religious teachings would be suspect and possibly heretical.

So what was suspect about Occam’s razor?

As McFadden explains, the dominant philosophy of William’s day, known as scholasticism, attempted to fuse Classical Greek metaphysics with Catholic theology. William used his razor to eliminate many of the constructs or entities used by the Scholastics, particularly the idea of universals.

In so doing he debunked their purported scientific proofs of the existence of God and a scientific basis for the miracle of the Eucharist. More importantly, he argued that since God transcends human reason (an omnipotent God is not bound by human reason and can do things that are incompatible with it) then God is unknowable through science. The only way to God is through faith and the scriptures. The reverse is also true, he claimed: knowledge of God acquired though faith and scriptures doesn’t tell you anything about the natural world.

William wielded his razor to split science irrevocably from theology.

According to one historian McFadden cites, “William provided the spark that lit both the Renaissance and the Reformation.” [p. 93]

The Pope may not have been amused, but the rest of us have benefited enormously.

Model Selection

In the second section of the book, McFadden presents the history of astronomy, starting with Ptolemy, and including Nicholaus Copernicus, Tycho Brahe, and Johannes Kepler. Each of them developed models of our solar system.

Ptolemy’s model was geocentric with the Earth at the center. Copernicus proposed a heliocentric model with the sun at the center. Tycho Brahe attempted to split the difference with a hybrid model placing the Earth at the center but with the planets orbiting the sun. Eventually Kepler produced his 3 laws of planetary motion, which more or less settled matters until Newton came along.

Each of these different models were able to explain and predict the motion of the moon and the planets to reasonable levels of accuracy for their time. So how to choose which one was better? 

McFadden shows us multiple occasions like this when scientists have many models to choose from, in some cases an infinite number of models. How do they evaluate them and decide which one is best?

Here’s another use for Occam’s razor: choose the simplest model that fits the facts.

Or, as McFadden beautifully puts it:

“William of Occam’s compass was his determination to reduce the parts list of the world to its minimum.” [p. 134]

Paradoxically, one of the benefits of simple models is that they’re usually easy to disprove. Yes, this is a benefit because easily disproved models don’t hang around very long before they are replaced by better ones. But you don’t know you need a better model until you disprove the one you’ve got.

Simplicity, Not Certainty

So just because a model is simple, how do we know it’s correct?

McFadden addresses this question in the last section of the book where he examines the work of Thomas Bayes, a Presbyterian minister who did fundamental work in the area of statistical probability.

McFadden explains the mathematics of Bayes’ work really well (you can read about it here). More importantly he shows how Bayes’ idea has come to influence model selection.

Faced with multiple models to choose from, Bayes’ work shows that the simplest model is the most likely to be correct.  McFadden calls this the Bayesian razor.

It’s critical to note here that neither Bayes, nor for that matter William of Occam, offer certainty.

Back in the 1300’s, William recognized that science could not offer proof, only hypotheses. For him, God’s existence was certain, but hypotheses could be disproved by new evidence. Bayes takes this a step further by providing a way to sift through a multitude of competing hypotheses. 

“… although Occam’s razor has many different manifestations and justifications, I believe the Bayesian razor expresses its essence, as applied to science. The razor favors the simple theories not because they are more beautiful, though they often are; not because they are easier to understand, though they usually will be; nor that they make fewer assumptions, though they usually do; or because they make tighter predictions, though they always do: but because they are more likely to be true.” [p. 306]

I think the idea that science doesn’t provide certainty, it can only lead us to ever-more-likely hypotheses is one of the most important and yet difficult concepts to grasp.

Maybe it’s because we so desperately want certainty.

It’s why you often hear people say, “well X is only a theory,” (insert evolution, climate change, vaccine effectiveness, etc.) when they want to dismiss the validity of said theory. Yes, they may only be “theories” but they’re the ones supported by the best available evidence we have today. And the simplest ones are the most likely to be true.

Our world is becoming increasingly complex and difficult to understand. In fact, the history of the universe is a story of increasing complexity. Perhaps one of the greatest achievements of science is that it has been able to find the simplest possible explanations for all that complexity. 

Life Is Simple is one of the better histories of science I’ve read. I like how McFadden acknowledges that this history is unfairly dominated by European white men. There are some parts of the book that seem to take a long time to get back to Occam’s razor, but I think the journey is worth it. Occam’s razor and the quest for simplicity really are core to modern science and our modern worldview.

As McFadden says towards the end of the book:

“Nevertheless, it’s important to remember that our preference for simple solutions is mostly a modern development. Prior to William of Occam, the standard response to a problem was to throw additional entities at it. William of Occam was the first to insist on drilling down to the simplest solutions, a principle that has since become the bedrock of science and the hallmark of modernity.” [p. 306]