Human beings are organic machines, not spiritual prisoners trapped in cages of flesh and bone. There is some debate as to how far Nietzsche intended this strategy to extend. Some authors feel that Nietzsche's is an all encompassing theory, meant to explain all worldly processes, while others feel that it is more restricted in scope, being intended to apply only to organisms or even only to human organisms. Everything that exists falls on a continuum between matter and form. Pure matter can potentially be anything, but must await the imposition of some kind of actual form in order to realize that potential.
Pure form lies at the other extreme end of the continuum.
It is a formal substance possessing pure actuality and devoid of any matter. Pure form might be thought of as God, the unmoved mover, or simply that which actualizes the potential in all things. Between these two extremes lies composite substance. Composite substance is material substance through which formal substance acts. Everything in our immediate environment is a composite substance, including humans and other organisms.