Megaric denial of change
are all things one substance—one man, one horse, or one soul—or quality and that one and the same—white or hot or something of the kind? These are all very different doctrines and all impossible to maintain.
This just seems like hasty thinking. Clearly, they will reject Aristotle's essentialism and so they can easily answer Aristotle's reductio ad absurdum.
We, on the other hand, must take for granted that the things that exist by nature are, either all or some of them, in motion—which is indeed made plain by induction". — Πετροκότσυφας
This too seems like a weak argument. The obvious reply would be to make an analogy with space. We are only aware and experience our present location and while we experience our present location in space we are not aware of and experience other locations in space; however, it does not follow that the only location of space that exists is the location we experience. The same can be said of time. The fact that we seem to experience change does not mean that change is a real feature of the world- at least not any more than our experience of our current location demonstrates that that location is more real than other locations in space. Eternalism would save the Megaric school from Aristotle's experience based argument.
they treat being as if it had just one meaning — Πετροκότσυφας
They sound like monists and Aristotle's disagreement can be seen to stem from his different metaphysical framework; I am guessing this is the real issue between the two?
Aristotle employs the actuality-potentiality pair, through which he defines change as "the fulfillment of what is potentially, as such". The unmusical man is potentially musical and the fulfillment of this potentiality counts as change (from being unmusical to being musical). — Πετροκότσυφας
The thing is how does introducing potentiality and actuality solve the issue of whether change is real or not?
To play devil's advocate, one could respond to Aristotle and say that X could potentially
be in such and such way, since it is a logically possible state of affairs, and that X is actually
in such and such way by virtue of X being a part of the real world. In this case, potentiality is nothing more than an acknowledgment that things could be different; Trump is actually president, but Hillary Clinton potentially could have been president. How is it that by pointing out that the actual state of affairs could have potentially been different demonstrate the change is a real feature of the world?
Aristotle provides a similar argument to the one you make. — Πετροκότσυφας
Well, I try to answer the dilemma by positing the possibility of mereological atomism and it seems like Aristotle answers it differently.