unification

Unification refers to the process of combining separate parts into a single, coherent whole. The term is used across disciplines to describe efforts to reconcile differences, standardize representations, or develop a common framework that explains multiple phenomena.

In logic and computer science, unification is the problem of finding a substitution for variables that makes two expressions identical. If possible, the expressions are unifiable, and the most general unifier is the minimal substitution from which all others can be derived. Robinson's unification algorithm established a standard procedure. Unification underlies automated theorem proving, type inference, and logic programming (for example, Prolog).

In linguistics, unification is a mechanism in constraint-based grammars and feature theory. It merges information across features (such as number, gender, and case) to determine whether a sequence is well formed. Unification-based grammars, including HPSG, rely on the compatibility of features to build representations.

In physics, unification refers to explaining several phenomena with a single framework. The unification of electricity and magnetism into electromagnetism, and the electroweak unification of electromagnetic and weak nuclear forces, are notable milestones. Current work seeks a Grand Unified Theory that would also include the strong nuclear force; gravity remains outside such unification.

In social and political contexts, unification denotes merging separate entities into one organization or state, or aligning institutions across regions. Historical examples include the unifications of Italy and Germany in the 19th century. The term is also used in discussions of regional integration and supranational governance.