Hylomorphism (from Greek hyle, “matter,” and morphe, “form”) is the theory, originating with Aristotle, that physical substances are composites of matter and form. On this view, matter is the underlying stuff capable of taking on a given form, and form is the organizing principle that makes a thing the kind of thing it is. Neither component exists as a substance on its own; a substance is constituted by their union. The term and its precise scope are contested among interpreters, with debate over whether hylomorphism is best understood as a metaphysical, scientific, or logical doctrine; see hylomorphism-scope-debate.

Hylomorphism originates in Aristotle's Physics and Metaphysics, where it is developed partly in response to earlier Greek thinkers, including Parmenides' denial of change and the atomists' account of substance as configurations of indivisible particles. Aristotle's framework was elaborated and adapted throughout the medieval period, most notably by Thomas Aquinas, who applied it to questions in philosophical theology, including the nature of the soul and the resurrection of the body. The doctrine receded from prominence with the rise of early modern mechanistic and corpuscularian science in the sixteenth and seventeenth centuries, which rejected substantial form as explanatorily superfluous.

In contemporary philosophy, hylomorphism has seen renewed interest, particularly among philosophers of mind and metaphysicians working on the problems of material constitution, personal identity, and the relationship between physical and mental properties. Some contemporary authors present hylomorphism as a resource for articulating non-reductive accounts of mind and biological organisms, while others treat it primarily as a historical doctrine of limited application to current scientific frameworks. Disagreement persists over how literally to read Aristotle's matter-form distinction, and over whether it can be detached from his broader physics and biology; see hylomorphism-history.

• Traditional Aristotelian-Thomistic viewpoint - Holds that hylomorphism, as developed by Aristotle and refined by Aquinas, accurately describes the structure of physical substances, including living organisms, and that substantial form is a genuine explanatory principle irreducible to material composition. See hylomorphism-thomistic-viewpoint.
• Reductive physicalist viewpoint - Holds that talk of “form” can be fully cashed out in terms of physical structure, arrangement, or function, so that hylomorphism adds no explanatory content beyond what physics and chemistry already provide. See hylomorphism-reductive-physicalist-viewpoint.
• Neo-Aristotelian revivalist viewpoint - Holds that a suitably modified hylomorphism remains a live and useful framework for contemporary metaphysics, particularly for problems of constitution, identity, and the unity of organisms, without committing to Aristotle's outdated physics. See hylomorphism-neo-aristotelian-viewpoint.
• Eliminativist viewpoint - Holds that the matter-form distinction is a relic of an obsolete conceptual scheme that should be abandoned rather than revised, since modern science has no need of substantial forms. See hylomorphism-eliminativist-viewpoint.
• Process-relational viewpoint - Holds that hylomorphism's static matter-form dichotomy misdescribes reality and should be replaced or supplemented by frameworks emphasizing process, relation, or becoming. See hylomorphism-process-relational-viewpoint.

• Scope of the doctrine - Whether hylomorphism is properly a metaphysical, scientific, or logical doctrine, and whether it can be detached from Aristotle's broader physics and biology, remains disputed among interpreters. See hylomorphism-scope-debate.

• hylomorphism-history
• hylomorphism-scope-debate
• hylomorphism-thomistic-viewpoint
• hylomorphism-reductive-physicalist-viewpoint
• hylomorphism-neo-aristotelian-viewpoint
• hylomorphism-eliminativist-viewpoint
• hylomorphism-process-relational-viewpoint
• hylomorphism-soul-body-debate
• Aristotle
• substance-metaphysics

1. Aristotle, Physics, Book I-II, trans. R. P. Hardie and R. K. Gaye, in The Complete Works of Aristotle, ed. Jonathan Barnes (Princeton: Princeton University Press, 1984).
2. Aristotle, Metaphysics, Book VII-VIII, trans. W. D. Ross, in The Complete Works of Aristotle, ed. Jonathan Barnes (Princeton: Princeton University Press, 1984).
3. Thomas Aquinas, Summa Theologiae, I, q. 76, trans. Fathers of the English Dominican Province (New York: Benziger Brothers, 1947).
4. Christopher Shields, Aristotle (London: Routledge, 2007), chap. 4.
5. William Jaworski, Structure and the Metaphysics of Mind: How Hylomorphism Solves the Mind-Body Problem (Oxford: Oxford University Press, 2016).
6. Kathrin Koslicki, The Structure of Objects (Oxford: Oxford University Press, 2008).