alikeness

Alikeness is the quality of being alike or the degree of resemblance between things. It describes how closely two objects, persons, ideas, or events share features, appearance, or function. Alikeness can be absolute (exact sameness in all relevant respects) or relative (partial resemblance in selected attributes). The term is used across disciplines and everyday language to express similarity without implying identity.

Etymology and usage: from alike + -ness; attested in Middle English as alikenesse. In ordinary speech, it often denotes visual or semantic resemblance, as in statements about a portrait's alikeness to its subject or about two theories sharing a common structure.

Philosophy and science: alikeness is studied as a relation of similarity. Some theories treat similarity as a primitive notion; others define it in terms of attribute overlap or distance in a feature space. In mathematics, the related notions are congruence and similarity, formalized as equivalence relations or metrics; alikeness in this sense is typically modeled by quantitative measures or by logical predicates that express resemblance.

Law and arts: the term overlaps with "likeness" and is central to rights of publicity, where the subject's image or persona must be depicted with sufficient alikeness to be recognizable. In art and portraiture, achieving alikeness is a measure of success in representing the subject.

See also: likeness, similarity, resemblance, parity, identity.