What is real, the things we see and touch around us, or the ideas of those things? It seems obvious, but Plato argued that things, being merely transitory, don't really exist in the same way that eternal ideas do. Ever since then, this "idealist" position has been a major branch of philosophy.
It always bothered me, and I am thinking about it again as I read Schopenhauer make the same basic argument. If something exists in time, it is by definition transitory; everything in time is constantly changing, and there must be a time before and after it existed when the object did not exist. But the idea of this thing, the template for it, always exists; it even exists outside of time and space. Therefore, the idea is more real than the thing.
I have trouble with the concept of anything "existing" outside of time and space, but that's another argument that I'm not prepared to make at the moment. My more pertinent objection is that it is too hard to define any particular "thing" for me to accept the idea that a template for it could actually exist, much less be more real than the thing itself.
When I ponder the existence of "things" in general, I tend to think of utilitarian things first of all, such as chairs or cars. We all know a car when we see one, and most of us see dozens or hundreds of them in a day. But even if we dispense with the distinction between, say, cars, trucks, and vans, and agree that we will lump them all together under the rubric of "cars," it still is not at all clear on closer examination what a "car" actually is. Is a motorcycle a car? Clearly not, most people would say, but it is harder to say where to draw the line. You might say a motorcycle has only two wheels, thus it can't stand on its own, but adding a sidecar wouldn't make it a real car. Or a motorcycle doesn't have an interior space, but if we make a three-wheeler with sides to it, where you have to get into a sort of cockpit, is that a car? What if we make a three-wheeled car with two wheels in front (I have seen these on the road occasionally) and only enough space to seat one person; is that more or less of a car than a three-wheeled motorcycle with side panels?
Along similar principles, you could argue whether a golf cart is a car (it isn't legal on the road, but is legality really the essential feature of a car?), or a backhoe, or a military tank, or perhaps whether an "armoured car" is really a car. Or, you could take things in a different direction and ask if a toy car is a car. It certainly looks like a car, and the boy who plays with it calls it a car. It can't move on its own, but if I put a spring in it and make it run on a wind-up principle, does it become a car? It's too small to carry a person, so I might ask if I make it just big enough to carry a child whether it is a car? If not, how big does it have to be? Or what if I have something that undboutedly is a car, say a red Corvette, but I remove the engine. Is it still a car even though, like the toy car, it can't actually go anywhere? It has the potential to take an engine, but so does a cinderblock, if you define "potential" broadly enough. Is the Corvette more of a car because it was designed to carry a person? What if someone makes a model of a Corvette to go in a museum? It was never intended to carry a person, does not have a functioning engine, but in other respects it looks just like a Corvette. You could put a working engine in it and it would go, perhaps not nearly as well as a Corvette -- it might even break down after 2 blocks -- but how far does it have to go before it changes from a model into a real car?
This is perhaps not the best example of a "thing," because it is consciously designed and has a purpose in mind. What about something organic, say, a deer? It is harder to come up with marginal cases of a deer, but not impossible. Let's say this particular deer has no legs. Probably you would say it is still a deer. What if it has no head? Then it can't function, so it isn't a deer in the same sense, but we would still refer to it as a "dead deer" -- that is, a deer with particular attributes -- rather than a carcass of no particular qualities. What if we gave our legless deer bionic legs? Okay, he's still a deer. What if we give him a mechanical liver and a mechanical heart? What if we replace his bones, one at a time, with artificial material (imagine he is a very sickly deer and can't survive without the transplants)? What if we replace his skin and fur with artificial substances? He still has a deer brain, but we have remade every other part of him. Is a deer brain a deer? It is still capable of thinking as a deer does, and of commanding its parts to move just like a normal deer. What if we could take another deer and replace just the brain with a small computer that functioned exactly like a deer? Would it be more or less of a deer than our bionic deer with nothing original but its brain?
Or let's look at it from another perspective. When I think of a deer, I always imagine a white-tailed deer, but someone from Europe might think of a fallow deer. Are they both from the same idea of "deer"? They may have evolved from a common ancestor, but that doesn't mean much; after all, we also evolved from a common ancestor with deer, and no one thinks a human is a deer. Or what if two species of deer mate and produce a hybrid. Is it less of a deer because it doesn't fit into a species? What if a deer mates with another animal that is not a deer; what do we call the type of its offspring?
I don't want to suggest that there isn't such a thing as a deer. Obviously there is, and I know it because they eat the fruit off of my wife's trees every year. But I can't grasp what the "idea" of a deer would be. "Deer" is a name that we give to some animals that we see that share certain characteristics; there is no such thing as a perfect deer to serve as an archetype. It just doesn't have any meaning. And this same discussion could be advanced for any object whatsoever, from rocks to humans. Deer really exist, in the sense that there really are a large number of animals that share certain characteristics, but there is no ideal concept of deer that could substitute or serve as a template for them.
And, yes, I seem here to be supporting a Nominalist view of language, in which our words merely stand for things, and aren't things in themselves. When I read about the medieval Nominalists, I instinctively opposed them, but I find that here they seem to be in a stronger position. It is less clear when it comes to abstract concepts such as "square" or "justice" or anything else that has no concrete representation. To me, those are an entirely different order of "thing" that deserve their own discussion and their own logic. What I am disputing is Schopenhauer's (and hence Plato's) claim that things don't really exist. If they wanted to say that things only have a marginal existence qua things -- that something is only more or less a deer, more or less a car, never absolutely something -- that would be an argument that I could agree with. But they are saying something quite different. They are saying that these things, because they are transitory, are not actually "things" at all; that they are just temporary representations of permanent ideas. And that is an argument the force of which I can't grasp.