The Aristotelian theory of the composition of corporeal beings, adopted and perfected by the scholastics. All bodies contain two constituent principles, the one passive and indeterminate, the other active and determining. The first is primal matter, the second that which gives it a particular character, a specific nature, that is, what constitutes it a substance with its own peculiar qualities which distinguish it from every other substance. The theory is known by the technical term hylomorphism (Greek: hyla, matter; morphe, form).