The discussion around Occam’s razor (or more generally the principle of parsimony) is often framed in terms of “simple” or “simplest” and ironically that is a dangerous oversimplification. You often hear it presented as “the simplest explanation is the correct one” or even just “the simplest explanation is the best.” “Simple” is an ambiguous and hugely load bearing word here.
I think it helps to reframe it - and this is closer to the original wording anyway - as “when making an explanation you should introduce the fewest new assumptions possible” - let me give an example to show why this is important.
If I offer an explanation for the history of life on Earth, that it likely evolved from some primordial process around energy gradients that became self-replicating molecules and gradually life, and then it evolved through selective pressures over billions of years into countless forms of life with incredible diversity, and that these naturalistic processes alone can explain that history and that diversity… and a creationist merely offers “God did it”
The common misunderstanding of Occam’s razor could justify selecting the latter explanation as being simpler. You’re offering a complex process with incredible diversity and variation and construction over time. Your opponent is offering divine intervention. It sounds simpler. But it doesn’t introduce the fewest new assumptions. We can explain the history of life on Earth pretty well with a naturalistic model. Abiogenesis is a separable hypothesis which is somewhat speculative (a new assumption) but it’s a far more reasonable new assumption than invoking God because it’s grounded in our understanding of chemistry and not in wishful thinking. Our scientific explanation is relatively complicated. But it doesn’t require massive new assumptions. It uses things that we’ve established to be true (or at least extremely consistently good explanations that have held up time after time when tested) through repeated rigorous study and model building. In comparison, “God” is quite a bit less known and more contentious.
So “God did it” is simpler. That matches the lay misconception of the Occam’s razor better. Which is why the lay misconception is wrong. “God did it” requires a massive new assumption, which is why it actually violates Occam’s razor.
When Napoleon asked Laplace why he didn’t explain the role of God in his models of the solar system, Laplace said “I have no need of that hypothesis” – not that God doesn’t exist, but that his model of the solar system works without having to invoke God, so why invoke God? It makes the explanation worse. Less parsimonious. That was actually a bit of a bold example of scientific and philosophical rigor in a time when it was common to work God into every explanation unnecessarily to satisfy cultural expectations. But it was rigorous and exactly in the spirit of Occam’s razor.
Let me give you a hypothetical example. I go to the grocery store. I see my neighbor’s car in the parking lot. I go inside and see my neighbor shopping. After I’ve purchased my groceries and leave, I see my neighbors car is gone from the parking lot. When I drive home, I see his car in his own driveway. The most obvious explanation? He drove himself to the grocery store, bought some groceries, and drove home.
An alternate explanation? He drove to the grocery store to buy groceries, loaded the groceries into his car, and then an alien space ship showed up, lifted his car with a tractor beam, and flew him home, dropping his car off in his driveway. He unpacked his groceries and went inside.
These two competing explanations are the same number of steps (arguably, depending on how you define steps) and so they’re equally “simple”, but one is MASSIVELY preferred over the other. We know that people drive their cars to get places. It’s routine, it’s established. Introducing an alien space ship with a tractor beam is a MASSIVE new assumption. Two, actually. There’s no reason to assume that tractor beams are practical tech even for aliens. And what’s more damning is that it introduces no new explanatory power. The mundane explanation about driving home fully explains all observations. There is nothing the alien space ship explains that isn’t already explained. There is no reason to make the alien spaceship explanation. It adds nothing. And you might think “the driving home explanation is a little simpler anyway, so it would win anyway” and you’re right - I could probably come up with a more air tight example - but it’s somewhat irrelevant. The introduction of the new assumption of the alien space ship is the massive crime, not that it arguably increases the number of steps.
My opinion, this is what Occam’s Razor (and more broadly the principle of parsimony) were designed to say – examine why you’re adding elements to your explanation. when are they new assumptions? do those new assumptions give more explanatory power? if not, discard those new assumptions barring compelling evidence that would change how much explanatory power they offer.
