2. Two Reasons for the First Conclusion

332. For the first conclusion [n.328] argument is given as follows: the terms of motion must be incompossible (plain from Physics 5.3.7-10); therefore nothing of one term is anything that remains in the other, just as the incompossible is not in its incompossible.

333. If the position were held too that some quantity remained the same here, but the terms of change were the greater and lesser in the quantity remaining - this he himself rejects because “the subject and terms of motion must really differ;” but the quantity, and the greater and lesser in the quantity, do not really differ, “for it cannot be said that variation happens according to greater and lesser without variation happening as to the essence of quantity, since greater and lesser are only the quantum itself essentially.” In this way does he himself argue that the same whiteness cannot both remain in the change and vary from greater to lesser.

334. And the strength of this reasoning [n.332] rests on this, that the subject is really distinguished from each term, and in this especially that the subject remains under each term; but neither term remains under the other, since they are opposites.

335. Again, each part of what is rarer is rarer; therefore each part of what is rarer is greater in quantity; therefore each part is a quantum with a new quantity.

336. If you say that something altogether new does not follow but only something new as to a part - on the contrary: I take what the subject is of the part of quantity that is new; that subject is rarer than it was before (from the first proposition [n.335]); therefore it is greater than before; therefore too it is a quantum with a greater quantity; and consequently the new quantity, of which the subject is posited as subject, will be greater than the old quantity and yet not altogether other than it. Therefore, in the same way the quantity of the whole rare thing will be greater than the whole quantity of the dense thing, and yet not altogether new.

337. Here argument [sc. against this, n.336] is made in brief as follows. If the quantity that was before remains, I ask what subject it is in; only in the same as it was in before, because the accident does not migrate; therefore, the subject that was a quantum with this quantity before will now be a quantum with the same quantity. Therefore, it cannot, either in the whole of itself or in a part, be a quantum with another new quantity unless the same thing be at the same time a quantum with two quantities (which is impossible), or unless there is in the rarefaction an aggregation of new parts of the substance under the new quantity; and the aggregation of quantum parts with preexisting quantum parts is rarefaction. But this is nothing, because then no part of the rarer would be rarer formally; for an old part would not be rarer formally by the fact that another new part was made continuous with it.