A term used in linguistics, and especially in generative grammar, referring to a property claimed to be common for all languages, to demonstrate the validity of which is a main goal of linguistic theory. Universal grammar is the term used to identify the main aim of those who hold that the ultimate purpose of linguistics is to specify precisely the possible form of a human grammar – and especially the restrictions on the form such grammars can take. In their broadest sense, then, language universals are equivalent to the general design features of human language identified by some linguists under such headings as duality, creativity, reflexiveness and displacement. In this sense, universals provide a theory of the human language faculty - which is thought to be an important step in the task of understanding human intellectual capacities.

In early generative literature, two main types of universal are recognized. Formal universals are the necessary conditions which have to be imposed on the construction of grammars in order for them to be able to operate. They include such notions as the number of components, types of rules, ordering conventions (e.g. cycles), types of transformations and so on. Substantive universals, on the other hand, are the primitive elements in a grammar, required for the analysis of linguistic data, e.g. NP, VP, [+ grave], [+abstract]. Depending on the component of the grammar in which they occur, universals are referred to as ‘phonological universals’, ‘semantic universals’ (cf. ‘universal semantics’), ‘syntactic universals’, etc. Some of these categories may actually be found in every language, but it is not crucial to the notion of substantive universal that they should be. All that is required is that they be constructs which need to be defined by linguistic theory to enable cross-language generalizations to be made, i.e. they are not terms established for the analysis of just one language, but are capable of general application. The universal base hypothesis in generative linguistics states that all languages can be generated by using the same set of basic rules - thought whether these are seen as rules of the base syntactic component or as a set of semantic formation rules depends on the theory employed.

Other types of linguistic universal have been suggested. Quantitative studies have introduced the notion of statistical universals, i.e. constants of a statistical kind, such as a ratio of use between different structures. Implicational universals are generalized statements of the form ‘if X, the Y’, e.g. if a language has a word-order of a certain type, it will also have a verb structure of a certain type. Absolute universals are properties which all languages share; there are no exceptions. Relative universals are general tendencies in language; there may be principled exceptions.