Theta Role - Theta Roles and Thematic Relations

Theta Roles and Thematic Relations

The term Theta Role is often used interchangeably with the term thematic relations (particularly in mainstream generative grammar — for an exception see (Carnie 2006)). The reason for this is simple: theta roles typically reference thematic relations. In particular, theta roles are often referred to by the most prominent thematic relation in them. For example, a common theta role is the primary or external argument. Typically, although not always, this theta role maps to a noun phrase which bears an agent thematic relation. As such, the theta role is called the "agent" theta role. This often leads to confusion between the two notions. The two concepts, however, can be distinguished in a number of ways.

• Thematic relations express the semantic relations that the entities denoted by the noun phrases bear towards the action or state denoted by the verb. By contrast, Theta roles are a syntactic notion about the number, type and placement of obligatory arguments. For instance, in the sentence Fergus ate the kibble, the fact that there are two arguments (Fergus and the kibble) and Fergus must be capable of volition and doing the action and the kibble must be something that can be eaten is a fact about theta roles (the number and type of the argument). The actual semantic type of the argument is described by the thematic relation.
• Not all theoretical approaches use theta roles. Theta roles are largely limited to the Chomskyan versions of Generative grammar and Lexical-functional grammar. Many other approaches such as Functional Grammar, and dependency grammar refer to thematic relations directly without an intermediate step in theta roles.
• Only arguments of the verb bear theta roles; optional adjunct modifiers — even if they are prepositional phrases (PPs) such as on Friday or noun phrases (NPs) like "yesterday" — don't take theta roles. But almost all NPs (except expletives) express thematic relations.
• An argument can bear only one theta role, but can take multiple thematic relations. For example, in "Susan gave Bill the paper." Susan bears both Agent and Source thematic relations, but it only bears one theta role (the external "agent" role).
• Thematic relations are properties of nouns and noun phrases. Theta roles can be assigned to any argument including noun phrases, prepositional phrases and embedded clauses. Thematic relations are not assigned to embedded clauses, and prepositions typically mark the thematic relation on an NP.

One common way of thinking about theta roles is that they are bundles of thematic relations associated with a particular argument position. (Carnie 2006)