The Identity of Indiscernibles

Picture, if you will, a universe with nothing in it except two perfect spheres with exactly the same color, size, and weight--the same everything, in fact. Except that they aren't the same thing.

Or are they?

And if they aren't, what makes them different?

And what's the point of saying they're different if you can't tell them apart?

Meet Castor and Pollux. "Castor" and "Pollux" are the names we use for these wonderful spheres, even though they don't have names. (That's just one of those differences they don't have.) Castor and Pollux come from a famous philosophy article by Max Black.

The whole point of this line of thinking is to understand that things are not just the sum of their size, color, shape, location, etc. But one worry with this way of thinking is that it means there are differences between things that seem to make no difference. It turns out that John Locke thought that way--behind all of a thing's properties is its unseen, unknown substance.

But David Hume thought it's silly to believe in differences that make no difference. A lot of philosophers follow his way of thinking, and they don't believe in hidden identity or hidden substance like Locke did.

I like Locke, and sometimes I like Hume. You know what else I like? I likes me some Leibniz! Gottfried Leibniz thought things are not just the sum of their size, color, shape, location, etc.--there's a substance and essence beyond all that. He also thought that these essential differences make a difference.

I'm on his team.

Frankly, this whole thing is obscure metaphysics--it's lovely, but still obscure philosophy talk.

But it's not just that. The relevance is that things do have natures, or essences--a built-in identity deeper than their accidental characteristics. My favorite teacup could have had a broken handle, but it couldn't have been a functional shoe. I could have been a dentist, but not an orangutan.

If that's all true, then we can also talk about some stuff that really matters, like the idea that people have free will. We can even have unfashionable but important discussions of what possibilities are open to a being with boy parts--he can't be a girl--and whether a male-male romantic relationship is the kind of thing that can be a marriage or not. There are always some practical applications and moral questions in the vicinity of metaphysics.

But--honestly--the vast majority of the conversation of this topic is just very nerdy metaphysics.

I recently published an article touting the Leibniz way of thinking about this topic. Here it is. You can read it--if you can get a copy from a college library, and if you think you're nerd enough.