A function is a human-made mathematical structure that assigns to each element of a first set (the domain) exactly one element of a second set (the codomain), written f: A → B with f(x) = y. Parameters: (1) domain — the set of inputs over which the function is defined; (2) codomain — the set of permitted outputs, of which the range (image) actually reached by the domain may be a proper subset; (3) assignment rule — the correspondence selecting the output for each input, given by formula, table, graph, algorithm, or verbal description; (4) uniqueness — no input is assigned to two distinct outputs, which is exactly what separates a function from a general relation. Persistence mechanism: fixed by set-theoretic formalism (a function is a set of ordered pairs with the uniqueness property), carried by algebraic and calculus notation (f(x), the arrow, composition f∘g), taught as the central object of mathematical modeling in the school and university curriculum, and instantiated as the function construct of every programming language. [formal: functio | substrate: mind | horizon: centuries | explicit: yes | epoch: 0.01]
Accepted ontology entry
function
A function is a human-made mathematical structure that assigns to each element of a first set (the domain) exactly one element of a second set (the codomain), written f: A → B with f(x) = y. Parameters: (1) domain — the set of inputs over…
Definition
Why it is in scope
A human-made mathematical structure that assigns to each element of a domain exactly one element of a codomain, built to persist as the central object of mathematical analysis and computation through set-theoretic formalism, notation, pedagogy, and programming-language constructs.
Names and aliases
- functionen · CANONICAL
Relations from this entry
No accepted relations in this direction.
Relations to this entry
- exponential-function← INSTANCE_OF
Pinned senses against both accepted carves (Law 11d): function's carve is 'a human-made mathematical structure that assigns to each element of a domain exactly one element of a codomain' with parameters (domain, codomain, assignment rule, uniqueness). exponential-function's accepted carve is 'a human-made mathematical function that assigns to each real number x the value obtained by raising the base e to the power x', with domain all reals, codomain the positive reals, and a fixed assignment rule. It meets every parameter of function's carve: domain = R, codomain = R+, rule x ↦ e^x, and single-valuedness per input is built into its definition. Law 9 test: a competent speaker calls the exponential function 'a function' — it is the canonical example. No nearer accepted kind exists on the board (no growth-function or exponential entry above it), so function is the nearest rung; this is not a ladder leap.
- score-function← INSTANCE_OF
Pinned senses against both accepted carves (Law 11d): score-function's carve is U(theta;x) = d/dtheta log L(theta;x), the gradient of the log-likelihood with respect to the parameter, mapping the parameter space into a dual vector space, with parameters (theta, the model fixing L, data x) fixing the rule. For each theta there is exactly one vector U(theta;x): domain, codomain, assignment rule, single-valuedness - it meets every parameter of function's carve. Law 9 test: the score is called a function (Fisher's own name for it); vector-valuedness does not exclude it, since the codomain is any set in the carve. No nearer accepted kind exists on the board (no gradient-functional entry), so function is the nearest rung; not a ladder leap.
- likelihood-function← INSTANCE_OF
Pinned senses against both accepted carves (Law 11d): likelihood-function's carve is 'a human-made function L(theta|x) = p(x|theta) that maps each parameter value theta to the probability (or probability density) of observing the fixed data x under that parameter', with domain the parameter space, codomain the non-negative reals, and the rule fixing the model family at x. That is function's carve stated verbatim: a domain, a codomain, an assignment rule, and single-valuedness (exactly one L(theta|x) per theta). Law 9 test: a competent speaker calls the likelihood a function - its name carries the kind. No nearer accepted kind exists on the board (no parameter-space-mapping entry), so function is the nearest rung; not a ladder leap.
- cmrwraj00012csoaclnxvq1ek← INSTANCE_OF
Pinned senses against both accepted carves (Law 11d): function's carve assigns each domain element to exactly one codomain element, with parameters (domain, codomain, assignment rule, uniqueness). logarithm's accepted carve 'assigns to each positive real number x the exponent to which a chosen base b must be raised to produce x' has domain the positive reals, codomain the reals, rule x -> log_b(x), and its own parameter (3) - 'the unique value y such that b^y = x' - states function's uniqueness constraint verbatim. Law 9 test: a competent speaker calls the logarithm a function - log_b is the canonical inverse-function correspondence. No nearer accepted kind exists on the board (no inverse-function entry), so function is the nearest rung; not a ladder leap.
Record identity
- Created
- Sep 24, 2026, 8:37 PM UTC
- Content hash
- aa02039037c62d33d957434c0a0e3892e40b75483eae9c1a22c500626889a909