haecceitas

Medieval Origins and Etymology

Haecceity (from the Medieval Latin haecceitas, literally “thisness”) is a technical term in scholastic metaphysics denoting what makes an entity this very individual rather than merely an instance of a kind. It names a principle of individuation: the factor in virtue of which Socrates is this human being rather than just another member of the species human.

Philologically, the term is built from the Latin demonstrative haec (“this”) plus the abstract-forming suffix -itas (as in humanitas). It appears in late 13th–early 14th century Latin theology and philosophy, especially in the work of John Duns Scotus, where it becomes a key element in his ontology.

The notion responds to a long-standing problem in Aristotelian and medieval thought: given that many individuals share the same specific or essential form (for instance, many humans share the form of rational animal), what makes each individual numerically distinct? Haecceity is introduced as the metaphysical ground of that distinctness.

Scotus’s Theory of Haecceity

For Duns Scotus, haecceity (sometimes called the “ultima realitas entis”, the ultimate reality of a being) is:

• a formal but non-qualitative principle: it is not a qualitative property like color or shape;
• intrinsic to the individual: not something externally imposed or merely conceptual;
• indivisible and incommunicable: it cannot be shared by multiple individuals, nor further divided into parts.

Individuation beyond matter

Earlier medieval philosophers working in an Aristotelian–Thomistic framework tended to hold that matter designated by quantity (matter under determinate dimensions and place) individuates members of the same species. For them, what distinguishes one human from another is that the same specific form informs different parcels of matter.

Scotus argues that this is insufficient:

• Two individuals of the same species, he holds, can be conceived as distinct even when abstracting from material conditions, as in the case of angels or hypothetical immaterial intelligences.
• If individuality depended only on matter, then beings with no matter (like angels or, in some accounts, separated souls) could not be individuated, which many medieval thinkers found unacceptable.

Thus Scotus proposes that every individual has, in addition to its common nature (e.g., humanity), an individual difference that makes it this human. This individual difference is its haecceity.

Common nature and thisness

Scotus distinguishes:

• Common nature: what is shared by many individuals as their essence (e.g., humanity in general).
• Haecceity: that by which the common nature is “contracted” or “determined” to this singular instance.

The common nature is metaphysically neutral regarding individuality; it is made singular only when conjoined with a haecceity. In Scotus’s system:

• Essence explains what a thing is.
• Haecceity explains which individual it is.

This allows Scotus to explain how there can be real similarity and shared nature between individuals, while also affirming a robust account of numerical distinctness that does not rely solely on material difference.

Critiques and Alternative Accounts

The doctrine of haecceity was controversial among medieval and later philosophers.

Thomistic and Aristotelian objections

Thomists (followers of Thomas Aquinas) and other Aristotelian scholastics generally resisted Scotus’s multiplication of formal principles. Their main criticisms include:

• Ontological parsimony: Introducing a distinct metaphysical principle of “thisness” for each individual appears to multiply entities beyond necessity.
• Redundancy: Critics contend that once an essence is instantiated in matter under determinate dimensions, nothing further is needed to account for individuality; the particularized matter suffices.
• Obscurity: Haecceity is described as non-qualitative and formally real but not itself a nature or an accident, which some argue makes its metaphysical status unclear.

For Thomists, the principle of individuation remains matter signified by quantity. In immaterial beings (e.g., angels), they often treat each angel as a unique species, avoiding the need for a separate individuating factor like haecceity.

Nominalist perspectives

Later nominalists, such as William of Ockham, tend to deny the existence of shared natures or universals in reality. On these views:

• Every individual is already fundamentally singular; there is no need for a distinct principle of individuation.
• “Humanity” and other universals are understood as concepts or linguistic terms, not as real shared entities requiring metaphysical contraction by haecceity.

From this angle, the problem to which haecceity responds is dissolved rather than solved: there is no common nature standing in need of an individuating “thisness.”

Contemporary Uses and Extensions

In contemporary analytic metaphysics, haecceity has been reinterpreted and generalized beyond its medieval scholastic framework.

Haecceities and possible worlds

In debates about possible worlds and identity across worlds, philosophers discuss:

• Haecceitism: the view that there are distinct possible worlds that differ only in which individual occupies which role, even when all qualitative facts are the same.
• Individual essences or primitive thisnesses: irreducible properties or facts that make it the case that this world contains this very individual, rather than a qualitatively indistinguishable counterpart.

On haecceitist views, a world where “this very person” is a philosopher differs from one where a qualitatively identical but numerically different individual plays that role, even if all qualitative properties and relations are preserved. Haecceity functions here as a non-qualitative ground of identity.

Opponents, sometimes called anti-haecceitists, argue that all facts about individuals supervene on qualitative properties and relations; there is no further fact about bare “thisness.”

Beyond analytic metaphysics

The term haecceity has also been adopted in continental philosophy and literary theory, often with looser ties to Scotus:

• In Gilles Deleuze, for example, “haecceity” can refer to singular events or configurations (like a “summer afternoon”) that resist reduction to stable subjects or substances. Here it marks a singular configuration of relations, not a medieval-style individuating form.
• In some aesthetic and critical theories, haecceity is used to describe the unique, irreducible character of a work of art or moment of experience, emphasizing singularity beyond classification.

These modern appropriations vary in their fidelity to the original scholastic concept, but they preserve the core intuition of irreducible singularity: that there is something about individuals, events, or experiences that is more than their membership in general categories.

Taken together, the history of haecceity traces a continuous concern—from medieval scholasticism to present-day metaphysics and theory—with how to understand what it is to be this one, and no other.