In Book II, Chapter 1 of the Physics Aristotle attempts to distinguish natural objects from artifacts. He begins by stating that a natural object ‘has in itself a source of change and staying unchanged, whether in respect of place, or growth and decay, or alteration’. But this is not sufficient to distinguish natural objects from artifacts. As he points out later, a wooden bed, for example, can rot or burn, and this is surely a change whose source is, in part, (...) internal to the bed. To make his distinction, Aristotle writes that in a natural object the internal ‘source of change and remaining unchanged’ belongs to it ‘primarily and of itself, that is, not by virtue of concurrence’. The bed rots because it happens to be made of wood: the change is due to its material, not due to its essence, namely that it is a bed. A natural object, however, changes because of its essence, that is, because it is the natural object that it is. (shrink)