Grognor draws the following picture, and says that we are much more likely to err by treating two things as one than by treating one things as two, because our limited mental faculties make one thing much easier to deal with than two. He praises making distinctions as harder and more important.
The point I want to press upon you is that the situations in the top row are easier or more likely than the situations in the bottom row, due to working memory constraints. An ontology with fewer objects in it is easier to understand, so it’s relatively easy for humans to correctly identify that what they thought was two things is actually one thing, and correspondingly, to mistakenly conflate two things into one. Mutatis mutandis, it’s hard for people to notice subtle distinctions. And likewise people have low propensity to mistakenly think that one thing is two things.
I’m not convinced.
For one thing, seeing two superficially dissimilar things as the same in a useful way requires dealing with large spaces of things and characteristics. So I don’t think the difference between one and two items in the question should be a deciding factor in how computationally hard the problem is for a brain. Figuring out how a raven is like a writing desk is way harder than imagining a raven and also a writing desk.
Also, this argument doesn’t distinguish between the upfront costs of seeing one thing as two or two things as one, and the long term costs. I think there are a very large class of things where there is a substantial upfront mental effort to see two things as the same, so we don’t. You can’t just go around mistaking a field of emus for a corporate office. However if you put careful thought into it, you might find that both represent a similar game theoretic situation. And once that has been noticed, it is relatively cheap to notice again in future. If it is true that seeing two things as one is less mentally taxing than seeing them as two, then those who originally make it easy to see two disparate things as one should get credit for making this easier for others later.
Also, I think it is often much more valuable to see two things as analogous that were not than it is to distinguish two things. Distinguishing things usually means deciding that the way you were treating both of them is not quite applicable to both, and you should treat at least one differently. But if you are only noticing this now, it probably wasn’t *that* inapplicable, and now you have to come up with a new way to deal with the thing. (I don’t have examples here, and I’m probably missing other useful effects of distinguishing things, e.g. relating to understanding them.) But treating what were previously two things as the same things means you get to port a whole bunch of things that you learned from one context into another context for free.
Grognor says that science means division. Maybe i’m biased, but I like the bits of science more that are about unifying. Physics over taxonomies. Which is perhaps just because our brains are small. But they really are.