This post is the fruit of yet another religion/philosophical debate on the Wesnoth forums. They’re often productive, in that it helps you to clarify your own arguments, though no one is ever persuaded to the other side.
Nominalism is often spoken of simply in terms of properties of objects – it would say, for example, that there is no property of ‘redness’ that an apple possesses, we just perceive it as ‘red’. But nominalism, which implies that nothing exists outside of the material world, also implies that there is no such thing as an “apply” to have “redness”. Basically, it seems to me that, if you don’t believe in anything other than the material world, there’s no reason to believe in the existence of anything as distinct from everything surrounding it.
I kind of need a reference picture to explain this:
We can all, I hope, agree that the upper-left-hand drawing is what, in essence, the world looks like: a bunch of atoms (which are composed of N, P and e, which are made of quarks and leptons, and probably so on and so on, though we don’t know yet) arranged in various ways. Consider the red dots subatomic particles of some sort.
Now, look at the upper-right-hand drawing; there, we group them into what we call an atom, and also into what we call a nucleus. But we’re no more justified in doing that than in grouping them like I have in the lower-left-hand drawing – sure, it seems to make more sense our way, but in a materialistic world there’s no “atom-ness” that our desired grouping has that my alternate grouping doesn’t.
So what I do is say that they have some non-material property that divides them into the proper objects. The particles in the nucleus aren’t physically green, and the electrons aren’t physically green, but they have some non-physical property, represented here as coloration, that makes them an object, and makes the alternate grouping not acceptable. In Platonic terms, there is a Form of Atom and Nucleus that these particles conform to, and thus they are an atom and a nucleus, not something else.
This ability to group objects into larger objects, which isn’t allowed in nominalism, is what lets me say that there is actually such a thing as “me”, as “you”, etc, as opposed to just a bunch of particles doing stuff.
The main problem with realism seems to be the Ship of Theseus problem and related paradoxes. I really don’t know how to answer those objections, yet. But realism still seems preferable because with nominalism, well, nothing actually exists so we can’t really talk about much of anything… I’ll post back later if I find an argument against the Ship.