 In addition to disputing the correct interpretation of these passages where Aristotle explicitly mentions prime matter, much of the debate has centered around, on the one hand, whether what he says about change really commits him to it, on the other, whether the idea is really absurd. Some opponents of prime matter have argued that Aristotle does not, after all, wish to insist that there is always something which persists through a change (see Charlton 1970, Appendix, and 1983). In particular, when one of the elements changes into another, there is an underlying thing—the initial element—but in this case it does not persist. They point out that in the key passage of Physics i 7, where Aristotle gives his account of change in general, he uses the expressions “underlying thing” and “thing that remains”. While readers have usually supposed that these terms are used interchangeably to refer to the substance, in cases of accidental change, and the matter in substantial changes, this assumption can be challenged. In the elemental generation case, perhaps there is no thing that remains, just an initial elements that underlies. The worry about this interpretation is whether it is consistent with Aristotle’s belief that nothing can come to be out of nothing. If there is no “thing that remains” in a case of elemental generation, how is an instance of water changing into air to be distinguished from the supposedly impossible sort of change whereby some water vanishes into nothing, and is instantly replaced by some air which has materialized out of nothing?