Aristotle distinguishes between actuality and potentiality.
If we take a bronze statue (the example at the Stanford Encyclopedia of Philosophy's Article on Aristotle and Causality), what is this statue actually and potentially?
Let's say it is potentially green, because after some time exposed to wind and weather, chemical reactions with the copper in the bronze will give rise to a green patina:
But is this statue potentially pink, too? After all, if somebody paints it pink, it will be pink.
Lets say a mad scientists invents a device that can easily turn less valuable metals like copper and tin into gold. Also, this device can turn the tin/copper atoms into gold atoms "in place" (afaik there is nothing physically impossible about that). With such a device we could turn our bronze statue into a gold statue. So is our bronze statue potentially golden?
Now we can further ask if we melt the statue and make a giant plate out of it, is the statue potentially circular? Ok, that would destroy the statue (using the common-sense understanding of destroy. I have no idea how we define destroy rigorously), so maybe that doesn't work. But if we would allow even that, the statue is potentially nearly everything. With a device powerful enough we might even turn it into a living thing!
To sum it up, the question is:
In Aristotelian metaphysics, what are the constraints of what a thing can potentially be? If a thing is potentially X because it is not physically impossible to turn it into a thing with property X, potentiality seems to be a meaningless term.