 Now imagine some particular substance, say, me. Suppose I go from being pale to being tan. Now it is still I who exist both before and after the sun has had its characteristic effect on me. This illustrates an important feature of substances: they can successively have contrary accidents and yet retain their numerical identity. This sort of change is known, appropriately enough, as accidental change. In an accidental change, a substance persists through the change, having first one accident and then another. But clearly not all changes are accidental changes. There was once a time when I did not exist, and then I came into existence. We can’t analyze this change as an accidental change, since there doesn’t seem to be any substance that persists through the change. Instead, a substance is precisely what comes into being; this is not an accidental but a substantial change. And yet there must be something that persists even through substantial change, since otherwise we wouldn’t have change at all; substances would come to exist from nothing and disappear into nothing. Scotus follows Aristotle in identifying matter as what persists through substantial change and substantial form as what makes a given parcel of matter the definite, unique, individual substance that it is. (There are also accidental forms, which are a substance’s accidental qualities.)