Lexical functional grammar (LFG) is a grammar framework in theoretical linguistics, a variety of generative grammar. It is a type of phrase structure grammar, as opposed to a dependency grammar. The development of the theory was initiated by Joan Bresnan and Ronald Kaplan in the 1970s, in reaction to the direction of research that transformational grammar was taking. It mainly focuses on syntax, including its relation with morphology and semantics. There has been little LFG work on phonology (although ideas from optimality theory have recently been popular in LFG research).