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.
History The notion of semantic roles was introduced into theoretical linguistics in the 1960s, by Jeffrey Gruber and Charles Fillmore. Additionally, Jackendoff did some early work on it in 1972. The focus of these studies on semantic aspects and how they affect syntax was part of a shift away from Chomsky's syntactic-centered approach, and in particular the notion of the autonomy of syntax, and his recent Aspects of the Theory of Syntax (1965).
Major thematic relations The following major thematic relations have been identified:
Agent Deliberately performs the action (e.g. Bill ate his soup quietly). The actions can be both conscious or unconscious (but unconscious actions are sometimes Force rather than Agent). In syntax, the agent is the argument of a transitive verb that corresponds to the subject in English. Experiencer The entity that receives sensory or emotional input (e.g. Susan heard the song. I cried). Stimulus Entity that prompts sensory or emotional feeling – not deliberately (e.g. David loves onions!). Theme Undergoes the action but does not change its state (e.g. I have two children. I put the book on the table. He gave the gun to the police officer. Percival saw the ball.) (Sometimes used interchangeably with patient.) In syntax, the theme is the direct object of a ditransitive verb. Patient Undergoes the action and changes its state (e.g. The falling rocks crushed the car.). (Sometimes used interchangeably with theme.) In syntax, the patient is the single object of a (mono)transitive verb. Instrument Used to carry out the action (e.g. Jamie cut the ribbon with a pair of scissors.). Force or natural cause Mindlessly performs the action (e.g. The water destroyed my computer.). Location Where the action occurs (e.g. Johnny and Linda played carelessly in the park. I'll be at Julie's house studying for my test.). Direction or goal Where the action is directed towards (e.g. The caravan continued on toward the distant oasis. He walked to school.). Recipient A special kind of goal associated with verbs expressing a change in ownership, possession (e.g. I sent John the letter. He gave the book to her). In syntax, the recipient or goal is the indirect object of a ditransitive verb. Source or origin Where the action originated (e.g. The rocket was launched from Central Command. She walked away from him.). Time The time at which the action occurs (e.g. The pitcher struck out nine batters today.) Beneficiary The entity for whose benefit the action occurs (e.g. I baked Reggie a cake. He built a car for me. I fight for the king.). Manner The way in which an action is carried out (e.g. With great urgency, Tabitha phoned 911.). Purpose The reason for which an action is performed (e.g. Tabitha phoned 911 right away in order to get some help.). Cause What caused the action to occur in the first place; not for what, rather because of what (e.g. Because Clyde was hungry, he ate the cake.).
There are not always clear boundaries between these relations. For example, in "the hammer broke the window", hammer might be labeled an agent, an instrument, a force, or possibly a cause. Nevertheless, some thematic relation labels are more logically plausible than others.
Grouping into the two macroroles of actor and undergoer In many functionally oriented linguistic approaches, the above thematic roles have been grouped into the two macroroles (also called generalized semantic roles or proto-roles) of actor and undergoer. This notion of semantic macroroles was introduced by Van Valin's Ph.D. thesis in 1977, developed in role and reference grammar, and then adapted in several linguistic approaches. According to Van Valin, while thematic roles define semantic relations, and relations like subject and direct object are syntactic ones, the semantic macroroles of actor and undergoer are relations that lie at the interface between semantics and syntax. Linguistic approaches that have adopted, in various forms, this notion of semantic macroroles include: the Generalized Semantic Roles of Foley and Van Valin Role and reference grammar (1984), David Dowty’s 1991 theory of thematic proto-roles, Kibrik's Semantic hyperroles (1997), Simon Dik's 1989 Functional discourse grammar, and some late 1990s versions of Head-driven phrase structure grammar. In Dowty’s theory of thematic proto-roles, semantic roles are considered as prototype notions, in which there is a prototypical agent role that has those traits characteristically associated to it, while other thematic roles have less of those traits and are accordingly proportionally more distant to the prototypical agent. The same goes for the opposite pole of the continuum, the patient proto-role.
Relationship to case In many languages, such as Finnish, Hungarian, Turkish, and some Asiatic languages like Korean and Japanese, thematic relations may be reflected in the case-marking on the noun. For instance, Hungarian has an instrumental case ending (-val/-vel), which explicitly marks the instrument of a sentence. Languages like English often mark such thematic relations with prepositions. In Korean, agents or other subjects are often marked with -이/-가 (-i/-ga), while -을/-를 (-eul/-reul) indicates a patient, theme, or other object.
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