Lexical Functional Grammar (LFG) was developed in the 1970s by Joan Bresnan and Ronald Kaplan to create a theory that could form the basis of a realistic model for linguistic learnability and language processing. LFG analyzes sentences using three structures: lexical structure uses grammatical functions to label argument structure; constituent structure encodes hierarchical groupings and categories; and functional structure integrates lexical and structural information to unify representations.