From this, too, we can see that the form is the universal, the matter the particular. For the form is the Idea, and the Idea is the universal. To say that form and {276} matter cannot exist apart is thus the same as saying that the universal only exists in the particular, which, as we have seen, is the fundamental note of Aristotle's philosophy. But if we thus identify matter with the particular element in things, we must be careful that we do not confuse the particular with the individual. We often use these two words as practically synonymous, and there is no harm in this, but here we must be careful to separate them. For every individual is, according to Aristotle, a compound of matter and form, of the particular and the universal. And when we say that matter is the particular, we mean, not that it is such a compound, but that it is the absolutely particular which has no universal in it. But the absolutely particular and isolated does not exist. A piece of gold, for instance, only exists by virtue of its properties, yellowness, heaviness, etc., and these qualities are just what it has in common with other things. So that the particular, as such, has no existence, but this is only the same as saying, what we have already said, that matter has no existence apart from form. A very natural mistake would be to suppose that by matter Aristotle meant the same as we do, namely, physical substance, such as wood or iron, and that by form he meant simply shape. Now although there is a kinship in the ideas, these two pairs of ideas are far from identical. Let us begin with matter. Our ordinary idea of matter as physical substance is an absolute conception. That is to say, a thing which we call material is absolutely, once and for all, matter. It is not material from one point of view, and immaterial from another. In every possible relation it is, and {277} remains, matter. Nor does it in process of time cease to be matter. Brass never becomes anything but matter. No doubt there are in nature changes of one sort of matter into another, for example, radium into helium. And for all we know, brass may become lead. But even so, it does not cease to be matter. But Aristotle's conception of matter is a relative conception. Matter and form are fluid. They flow into one another. The same thing, from one point of view, is matter, from another, form. In all change, matter is that which becomes, that upon which the change is wrought. That is form towards which the change operates. What becomes is matter. What it becomes is form. Thus wood is matter if considered in relation to the bed. For it is what becomes the bed. But wood is form if considered in relation to the growing plant. For it is what the plant becomes. The oak is the form of the acorn, but it is the matter of the oak furniture.