Putting the green back in the greenery

......The green of the greenery seems to be out there with that greenery. But what is out there is the surfaces of leaves, which send electromagnetic waves toward our eyes. The green is in the pictures of the world that our brains construct from data obtained via our sensory organs. What about the shapes of the leaves? Could the world be made of 10-dimensional strings, with our brains imposing upon the numerous sensations that come from our 10-dimensional sensory organs the shapes that we see in the world around us? Maybe; and for such reasons, some philosophers think that ordinary objects don’t exist in reality.
......Does the world (what we usually mean by ‘the world’) only exist in our heads? Well, there are certainly some ordinary objects in reality: what we mean by ‘reality’ is whatever space it is that includes the people whose language includes such expressions, so you and I are presumably two people (whatever we are made of). And there is a sense in which the greenness really is out there on the surfaces of leaves, because we learn the meaning of ‘green’ by being shown various green objects (or pictures of green objects) and being told that they are all green. It hardly matters whether you and I have the same sensations when we see them. Green is something that ordinary objects can be. Still, green is also a sensation. And a very mysterious one: do you have the same sensation as I do, when we both look at the same leaf? We have similar eyes and brains, but we know nothing about how sensations arise in our brains. Still, something is green if its surface is such that under normal lighting conditions, it would give rise to the same sort of sensations in those looking at it as they had when they learnt the meaning of ‘green’ whatever those sensations are.
......If your sensation when you see green was exactly the same as mine when I see blue, would I be wrong if I thought that you were seeing blue? Well, it seems to me that the meaning of ‘blue’ is the sensation that I have when I see blue things. But it also seems to me that the meaning of words like ‘blue’ is a public, not a private matter. So it seems to me that there is something like an equivocation here. And it seems to me that it is probably unavoidable, because our references to things in our external world are only possible via our sides of our interactions with those things. Would it be any different in the land of the blind? Suppose that they use sticks there, to feel their way around. And suppose that one of their sticks hits an unexpected obstacle. The person holding that stick might be able to tell that the other end of it had hit a bouncy object. And their word for such bounciness in an object might be the same as their word for the way that that stick had felt in that hand. But they would of course not think of the world as being full of such feelings. They would think of it as being full of objects, mysterious objects, some of them bouncy (in some non-visual sense of ‘bouncy’).
......When a tree falls in a forest at night, and there is no one around to hear it, does it make a sound? I suppose not, but what about its colour? Those trees do not look green: it is dark, and there is no one there to see them anyway. But they are green in the daytime, so I suppose that they are green trees. Suppose that you have a colour photograph of those trees on your wall. You do not think that those trees are there, in your room, but the green of those trees is there. Is it still there when you turn the light off and leave the room? Suppose that you return with a strange little light bulb: you change the bulb, turn the light on, and in that light the photograph looks blue. Is it a green photograph that looks blue? Is it still green, even though it looks blue in the strange light? And did other people learn words like ‘green’ in such a way that they would give similar answers to such questions?
......It is not implausible that philosophers could disagree about the "existence" of ordinary objects without any of them being wrong! What is clear is that a green alarm clock that goes off in a vacuum makes no sound. And if the clock is painted black, then it is no longer green. And such rooms exist in houses that are quite distinct from each other. Your house and my house are two houses, in a very precise way. When we reason logically about the world, our thoughts are as complicated as our relationships with the world. But the simplest thing to reason logically about ought to be arithmetic.