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. This modification eliminates the possibility of any pure matter or form. Everything that exists, in this schema, has to be a composite substance, and nothing exists that isnt composite. Caught in a Heraclitean struggle of opposites, the world emerges in an eternal process of actualizing potentialities. The question of God's existence as a pure, formal substance, or the question of the existence of any kind of fundamental, material substance is eliminated from this picture.