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In a number of theories of linguistics, thematic relations is a term used to express the role that a noun phrase plays with respect to the action or state described by a sentence's verb. For example, in the sentence "Susan ate an apple", Susan is the doer of the eating, so she is an agent; the apple is the item that is eaten, so it is a patient. 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 been used analogously to 'thematic relation'.
Major thematic relations
Here is a list of the major thematic relations.
- Agent: deliberately performs the action (e.g., Bill ate his soup quietly.).
- Experiencer: the entity that receives sensory or emotional input (e.g. Susan heard the song. I cried.).
- Theme: undergoes the action but does not change its state (e.g., We believe in one God. I have two children. I put the book on the table. He gave the gun to the police officer.) (Sometimes used interchangeably with patient.)
- Patient: undergoes the action and changes its state (e.g., The falling rocks crushed the car.). (Sometimes used interchangeably with theme.)
- 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., An avalanche destroyed the ancient temple.).
- 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.)
- 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 rocket was launched yesterday.).
- 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 no clear boundaries between these relations. For example, in "the hammer broke the window", some linguists treat hammer as an agent, some others as instrument, while some others treat it as a special role different from these.
Relationship of case to thematic relations
In many languages, such as Finnish and Hungarian and Turkish, 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.
The term "thematic relation" is frequently confused with theta role. Many linguists (particularly generative grammarians) use the terms interchangeably. This is because theta roles are typically named by the most prominent thematic relation that they are associated with. To make matters more confusing, depending upon which theoretical approach one assumes, the grammatical relations of subject and object, etc., are often closely tied to the semantic relations. For example, in the typological tradition agents/actors are tied closely to the notion of subject (S). Here is a way to distinguish these ideas, when they are used distinctly:
- Thematic relations are purely semantic descriptions of the way in which the entities described by the noun phrase are functioning with respect to the meaning of the action described by the verb. A noun may bear more than one thematic relation. Almost every noun phrase bears at least one thematic relation (the exception are expletives). Thematic relations on a noun are identical in sentences that are paraphrases of one another.
- Theta roles are syntactic structures reflecting positions in the argument structure of the verb they are associated with. A noun may only bear one theta role. Only arguments bear theta roles. Adjuncts do not bear theta roles.
- Grammatical relations express the surface position (in languages like English) or case (in languages like Latin) that a noun phrase bears in the sentence.
Thematic relations concern the nature of the relationship between the meaning of the verb and the meaning of the noun. Theta roles are about the number of arguments that a verb requires (which is a purely syntactic notion). Theta roles are a syntactic relation that refers to the semantic thematic relations.
For example, take the sentence "Reggie gave the kibble to Fergus on Friday."
- Thematic relations: "Reggie" is doing the action so is the agent, but he is also the source of the kibble (note Reggie bears two thematic relations!); "the kibble" is the entity acted upon so it is the patient; Fergus is the direction/goal or recipient of the giving. Friday represents the time of the action.
- theta roles: The verb "give" requires three arguments (see valency). In generative grammar, this is encoded in terms of the number and type of theta roles the verb takes. The theta role is named by the most prominent thematic relation associated with it. So the three required arguments bear the theta roles (confusingly!) named the agent (Reggie) the patient (or theme) (the kibble), and goal/recipient (Fergus). "On Friday" does not receive a theta role from the verb, because it is an adjunct. Note that "Reggie" bears two thematic relations (Agent and Source), but only one theta role (the argument slot associated with these thematic relations).
- grammatical relations: The subject (S) of this sentence is "Reggie", the object (O) is "the kibble", the indirect object is "to Fergus", and "on Friday" is an oblique.
- Morphosyntactic alignment
- Case grammar
- Theta roles
- Semantic role labeling, a natural language processing task to automatically determine thematic roles
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