hylomorphism

Hylomorphism is a theory in Aristotle's metaphysics that holds natural substances are composites of matter (hyle) and form (morphē). Matter provides the substratum with potentiality, while form supplies organization, structure, and actuality. Substances are thus unified wholes whose properties and changes arise from the interaction of matter and form; neither aspect alone suffices to explain a thing’s existence. In this framework, the form is the governing principle that gives a thing its identity, while matter is what it is made of. Together they realize a thing’s being and, with the idea of causes, explain generation and change.

In Aristotle's account, matter and form are inseparable in individual substances. Change is described as a process by which form actualizes potential aspects of matter, preserving some aspects of the underlying substratum while reconfiguring its organization. The formal cause—the form—plays a central role alongside the material, efficient, and final causes in accounting for why a thing is the way it is and why it comes to be.

In biology and psychology, hylomorphism implies living beings are composites of matter with an intrinsic form; for animals and humans, the soul is the form of the body, the organizing principle that animates life. The soul, as form, endows the body with life and functioning without positing a separate, independent substance.

Medieval philosophers, notably Thomas Aquinas, adopted and adapted hylomorphism to Christian theology, arguing that human beings are substances composed of body (matter) and soul (form), with the soul serving as the form that animates and gives personal identity to the body.

Critics challenge the coherence of form as an explanatory principle and debate how form and matter interact. Nonetheless, hylomorphism remains influential in discussions of substance, change, and the mind–body problem, and persists in neo-Aristotelian approaches within philosophy.