transformational grammar, a system of language analysis that recognizes the relationship among the various elements of a sentence and among the possible sentences of a language and uses processes or rules (some of which are called transformations) to express these relationships.Transformational grammar assigns a "deep structure" and a "surface structure" to show the relationship of such sentences. Thus, "I know a man who flies planes" can be considered the surface form of a deep structure approximately like "I know a man.