Grammar, Comparative and general Topic and comment

In certain theories of linguistics, thematic relations, also known as semantic roles or thematic roles, are the various roles that a noun phrase may play with respect to the action or state described by a governing verb, commonly the sentence's main verb. For example, in the sentence "Susan ate an apple", Susan is the doer of the eating, so she is an agent; an apple is the item that is eaten, so it is a patient. Since their introduction in the mid-1960s by Jeffrey Gruber and Charles Fillmore, semantic roles have been a core linguistic concept and ground of debate between linguist approaches, because of their potential in explaining the relationship between syntax and semantics (also known as the syntax-semantics interface), that is, how meaning affects the surface syntactic codification of language. The notion of semantic roles plays a central role especially in functionalist and language-comparative (typological) theories of language and grammar. While most modern linguistic theories make reference to such relations in one form or another, the general term, as well as the terms for specific relations, varies: "participant role", "semantic role", and "deep case" have also been employed with similar sense.