What does it mean to be magic?
Magic for most people is something that washed over them, something they can channel, something they are able to harness. For ordinary people, and for those who would consider themselves un-ordinary as well, magic is a force of its own. And these people, ordinary or un-ordinary, would live in ordinary places, and be surrounded with ordinary magic, that which they could see and feel within their surroundings. But some do feel magic, are able to feel it within, and without. They could feel magic through every pore of their body, they could feel themselves in every miracle and dream. That's what it is to be a metamorphmagus, among others.
To feel magic shifting your every molecule. If you rearrange someone's internal being, are they still the same person? The answer, quite simply, is no. I hypothesize, however, that for a metamorphmagus, for an animagus, for those subjected to even certain transfigurations, magic takes a far more personal role.
I believe that it is magic that keeps their being from falling apart. Magic that holds the mind of the magic-user, even when they are in forms far detached from their original body. That so easily allows them to return to that form. With the knowledge of hormones, how is it that animagi can feel human emotions, in animal forms? With the knowledge of brains, how is it that they can think in human patterns in animal heads?
I think it becomes quite obvious that magic is the answer. Magic holds the very being of the user apart from their physical form, allowing them to transcend spatial limits. In a similar thread, what about the issue of portraits? They too hold the being of their subject, however they are unable to change. A picture can be described as an immortalized moment in time, however a magical portrait is an immortalized moment in time given thoughts, words, and sometimes even actions. What then, causes this great divide, that severs the portrait from the passage of time?
I regret giving it weight even now, this thought, but it plagues my mind, and will continue to do so until the question is spread into the world. Why are there no living portraits? A portrait holds a person's being, even their will. Portraits can have desires, and even act upon them. But why can they not change? Why can they not learn? The most likely answer that I have come to is that they don't contain the full being of their subject, merely a copy. A copy imbued with agency. But if one were to fully embody a portrait, to transform themselves much like an animagus…
I forget myself, and I can only apologize once more. To be magic, is to be reliant upon it. If a metamorphagus were to feel their own magic wane, if it were even to diminish in potency during a transformation, the result would be disastrous. The metamorph relies upon magic to return it to its previous form, and to guide it to its next. Without it, transformations could turn messy, have unexpected growths or disappearances, or simply become impossible. Some believe that metamorphs have a base form that they would naturally return to. I believe differently. I believe they have no form. And I believe that, bereft of magic, they would dissolve into nothingness.
Journal entry, 1931, Albus Dumbledore. On magic, and being.