  Still, it is noteworthy that this four-causal framework of explanation was developed initially in response to some puzzles about change and generation. Aristotle argues with some justification that all change and generation require the existence of something complex: when a statue comes to be from a lump of bronze, there is some continuing subject, the bronze, and something it comes to acquire, its new form. Thus the statue is, and must be, a certain kind of compound, one of form and matter. Without this type of complexity, generation would be impossible; since generation in fact occurs, form and matter must be genuine features of generated compounds. Similarly, but less obviously, qualitative change requires much the same apparatus: when a statue is painted, there is some continuing subject, the statue, and a new feature acquired, its new color. Here too there is complexity, and complexity which is readily articulated in terms of form and matter, but now of form which is evidently inessential to the continued existence of the entity whose form it is. The statue continues to exist, but receives a form which is accidental to it; it might lose that form without going out of existence. By contrast, should the statue lose its essential form, as would happen for example if the bronze which constitutes it were melted, divided, and recast as twelve dozen letter openers, it would cease to exist altogether.