Tagmetics. "The central concept is the tagmeme, defined by the relation between a syntactic 'slot' or function, such as subject or object, and a class of units, such as noun phrase or pronoun, that can 'fill' it. Constructions, or syntagmemes, are accordingly characterized by sequences of obligatory and optional tagmemes: e.g. that of The people were leaving by one in which there is an obligatory subject slot, filled by the noun phrase, followed by an obligatory predicate slot, filled by a verb phrase". Even though I don't understand it, it's still a beautiful word.