There are 3 concepts in Buddhism (specifically Mahayana philosophy) used to describe the relation between substance and it’s function. They are tai (body), hsiang (form), and yung (use). Body corresponds to substance, Form to appearance, and Use to function.
In this way we can say an apple is reddish and round shaped; this is it’s Form and further how it appeals to the senses. So Form belongs to the world of the senses; or the world or appearance.
Use represents what an object stands for, it’s value, utility and function.
Lastly, the Body is what constitutes the apples apple-ship, without which it looses it’s being; no apple, even with all of it’s appearances and functions is an apple without it.
To be a real object then, all three of these concepts must be accounted for. Sounds a bit like Subject, Object, Quality, doesn't it?
Following this then, and applying these concepts to ones self-nature and wisdom; Self-nature (self-knowledge; not being, but knowing, as knowing IS being) is the body, and wisdom (prajna) it’s use. In this case there is nothing corresponding to form because the subject does not belong to the world of form.
I'd like to further discuss these concepts while moving forward in my Religious Language posts (as these become key).