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