In his Metaphysics, Aristotle examines in greater detail the relationship between matter and form as well as the relationships between the various formal properties of that which exists ("being"). While Aristotle does maintain the primacy of form over matter, the dependency of form on matter is his main critique of Plato's ontology, according to which form is the only true being. In Plato, the material universe exists only as an inferior imitation of the forms as they exist in the immaterial world of Ideas. While Aristotle's view that substance is form clearly draws from Platonic doctrine, his insistence that form can exist only in conjunction with matter marks a radical departure from Plato's teachings.