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Aristotle on potential

Aristotle says that "the soul is the first actuality of a natural body that is potentially alive". DA2.1 412a27 [Check]

The idea has been interpreted as to do with capacity. The soul is a capacity, not a substance - the capacity to engage in activities characteristic of the kind of thing the thing is.

He has a second use for potential, and that is in connection with change. Plato's conception of forms led to a conception of change which presented great diffiuclties. Aristotle maintained instead that A can change into B in virtue of having even as A the potential to become B.

For him, for A to have the potential to become B it has got to be true that A could 'actually' become B. This places the emphasis on causality.

The thought might be:

Some change are possible and some aren't. Whatever it is that places this constraint, if there is one, it must be present in the thing before it changes, if it does. But of course this is completely invalid. If you take the view that no change happens unless circumstances change then to say A might change is simply to say that A's actual reality is such that such and such triggers will change it, and such and such triggers won't. No need of talk of potential in the Modern world - in this respect anyway.

In Aristotelian terms, Blackburn tells us, his Dictionary, entry for potential, "potential is a power to change into different states". He also points out that the notion has a decisive application in quantum mechanics.

What is the Scholastic understanding of change, against the background of their commitment to forms? A thing's form concerns its essential properties only, so a thing can change its accidental properties, no problem.

But what about one thing becoming another - a caterpillar becoming a moth? If we believe in forms you've got a problem (but we need to spell it out).