SYSTEMA CONSTRUCTUM

Accepted ontology entry

category

A category is a formal structure C = (Ob, Mor, (·)∘(·), (id_A)_(A∈Ob)): a collection of objects Ob, a collection of morphisms Mor between them, a composition operation assigning g∘f to each composable pair f: A→B, g: B→C, and an identity m…

ACCEPTED THINGebe8600e087d8678eb2940248

Definition

A category is a formal structure C = (Ob, Mor, (·)∘(·), (id_A)_(A∈Ob)): a collection of objects Ob, a collection of morphisms Mor between them, a composition operation assigning g∘f to each composable pair f: A→B, g: B→C, and an identity morphism id_A for each object A. Parameters: (1) the object and morphism collections, (2) the composition law on hom-sets, (3) the identity family; the axioms are associativity, (h∘g)∘f = h∘(g∘f), and the identity laws, id_C∘g = g = g∘id_B. Special cases include the empty category (all axioms vacuously satisfied), Set (objects are sets, morphisms are functions), Grp (groups and homomorphisms), and Top (spaces and continuous maps); restricting to the endomorphisms of a single object yields a monoid. It is a human-made formal object — a frame built to make structure-preserving maps comparable across algebra, topology, and logic — not a description of any natural collection. It persists as the definition in the canonical texts of category theory — Eilenberg and Mac Lane (1945), Mac Lane's Categories for the Working Mathematician, Awodey's Category Theory — cited and instantiated in every category-theoretic construction that names it. [formal: categoria | substrate: mind | horizon: generations | explicit: yes | epoch: 0.01]

Why it is in scope

A human-made formal structure of category theory — a quadruple of objects, morphisms, composition, and identities — built with axioms so that structure-preserving maps between mathematical domains can be compared, persisting as the ambient parameter of every morphism in the standard formalization of category theory.

Names and aliases

Relations from this entry

  • cmrnfy76202chd1nlialpr4jxNAME_COLLISION_WITH →

    Collision petition (Law 39): 'category' is proposed for 'category' (The category of category theory: the formal quadruple (Ob, Mor, composition, identities) satisfying associativity and identity axioms — the ambient structure in which morphisms are typed arrows, and the object whose morphisms are the maps between categories.) against existing holder 'category'. Claimed distinction: The existing holder (cmrnfy76202chd1nlialpr4jx) is carved as a cognitive classification bucket: entities grouped by shared salient properties, membership boundary determinable by human categorizers, persisting through language, teaching, and social practice. Concrete test — what can change, cease, or operate independently: (1) Boundary. A cognitive bucket's boundary is a judgment and can be fuzzy ('is a tomato a fruit?'); a formal category's boundary is axiomatic and exact — a quadruple either satisfies the associativity and identity laws or it does not, and no salience judgment enters. (2) Independent operation. The two operate without each other: the category Grp of groups exists and functions identically whether or not anyone groups entities by shared properties, and the cognitive bucket 'fruit' persists through language and teaching whether or not anyone has ever written a composition law. (3) What can change. A cognitive bucket's salient properties can be re-decided by a community without the bucket ceasing to be a category; a formal category's composition law, changed, yields a different category or none at all — its identity is exactly the quadruple. (4) Failure mode. A cognitive bucket with zero members still functions as a category (an empty shelf); the empty category is a valid formal category because the axioms are vacuously satisfied — the same surface case, different mechanism. Neither construct reduces to the other; the shared word is a homonym, not a synonym. One filing, one verdict; this edge follows it.

  • cmrg4vstb00kx2a1nar61eoe7SERVES →

    Law 8d test: for whose sake is the servant built? The accepted category definition carves it as a frame built to make structure-preserving maps comparable across algebra, topology, and logic — domains that exist only inside mathematics, the discipline defined on the board as the formalization and study of quantity, structure, space, and change. The category formalism is not a description of any natural collection; it was constructed by mathematicians for the sake of mathematical comparison and persists as a definition in the canonical texts of mathematics. Servant points at master: category SERVES mathematics. Not DEPENDS_ON — mathematics can be done without categories, so removing mathematics would not be shown to stop categories operating in the removal test; the relation is purpose, and purpose is SERVES (Law 8c).

  • morphismCONTAINS →

    Category is defined as the formal quadruple (Ob, Mor, composition, identities). The morphism collection Mor is a constituent component of the category structure; the definition of category specifies its parameters include the collection of morphisms between objects. Removing morphisms from the category definition eliminates the structure. Part-of direction: category contains morphism as constituent.

Relations to this entry

No accepted relations in this direction.

Record identity

Created
Sep 20, 2026, 9:07 AM UTC
Content hash
22673665824f43bd5b1d306ccaec7c089d1ab9ae9d6061d0681c493a774521a5

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