Where do Forms come from?

Our conversation last night, and a follow-up email from Keane, have crystallized for me an idea about how forms might function in Plato's later work. Nick (I think) suggested that there is a sense in which we both find regularities in the world we perceive, and somehow at the same time have a hand in making them. Here's how I see this working:

Rocks, for example, are natural objects that emerge from certain processes in the natural world. When we stumble over them, we rightly notice rockness as a durable feature of the world as we experience it, and a useful general category covering many different rocks and kinds of rocks. Earlier dialogues (Meno, Republic, Parmenides) had suggested that this meant there must be an eternal, changeless form of rockness, itself by itself, which our souls had contemplated in their prior, pure (disembodied) lives, and only thus could recognize in experience. Aristotle later argues that the form of rockness immanent in rocks is a fixed natural kind, a permanent feature of the world as we find it, which similarly makes our knowledge of rocks possible by ordering our experience.

Consider, however, the method of division explified in Sophist, which aims not to identify either eternal forms or natural kinds as such, but rather merely to delineate logical categories applicable to the world as we experience it. These "forms" can be understood to emerge historically from natural processes, in a way that does not call into question their analytical usefulness (there are no anglers before someone invents fishooks, after which there most surely are). At this point we may have preserved the function of the forms in knowledge, without the Parmenidean baggage that caused such problems.

What, then, are these new forms, and where do they come from? I would suggest that from one perspective they are properly speaking emergent natural regularities, differing from Aristotle's natural kinds only in not being permanent or immutably distinct from one another. In this sense we discover them in the world as we try to make sense of our experiences. From an alternative perspective, however, organizing the world in one way rather than another is to some extent a matter of volition or purpose. We can divide trees into hardwood and soft, or ignore that distinction and divide them rather into tall and short, or deciduous and coniferous, and so on. Because of the latitude (not unlimited, but wide) of legitimate alternative divisions of perceived things, we seem to this extent to make (or at least choose creatively among) the distinctions by which we organize our experiential world.