whatness

Whatness, or quiddity, is a philosophical term for the essential nature or definition of a thing—the properties that make it what it is. It is contrasted with contingent features the thing happens to have and with haecceity, the “thisness” that individuates a particular object.

Etymology: The word derives from Latin quidditas, literally “whatness,” pointing to the intrinsic nature that defines a kind.

Historical background: In Aristotle, essence is the form that gives a thing its kind and teleological explainability. In medieval scholasticism, quidditas denotes the intrinsic nature or essential form of a thing and serves as the principle of its being and intelligibility. In modern and contemporary philosophy, whatness remains central to discussions of essence, essential properties, and natural kinds, shaping debates about whether essences are real, discoverable, or merely useful hypotheses.

Distinctions: Whatness is often paired with haecceity, the individualizing “thisness” of a particular object, and with contingent properties that do not define the kind. Philosophers also distinguish between essential properties (those that must hold for the thing to be that kind) and accidental properties (properties it may lose without ceasing to be of the kind).

Contemporary use: Some theorists defend essentialist accounts in which kinds have necessary and sufficient conditions, while anti-essentialists argue that no fixed essence underwrites all instances. The notion of whatness continues to influence discussions of identity, classification, and scientific explanation.

See also: Quiddity, Essence, Haecceity, Essentialism, Natural kind.