Agent (grammar)

In linguistics, a grammatical agent is a thematic relation that refers to the cause or initiator of an event. The agent is a semantic concept distinct from the subject of a sentence. While the subject is determined syntactically, primarily through word order, the agent is determined through its relationship to the action expressed by the verb. The word comes from the present participle agens, agentis ("the one doing") of the Latin verb agere, to "do" or "make".

Typically, the situation is denoted by a sentence, the action by a verb in the sentence, and the agent by a noun phrase.

For example, in the sentence "Jack kicked the ball", Jack is the agent and "the ball" is the patient. In certain languages, the agent is declined or otherwise marked to indicate its grammatical role. In Japanese, for instance, the agentive case is marked with the case particle ga (が), while the nominative case, also called "bare case" or hadaka-kaku (ハダカ格), is marked with no case particle.Modern English does not mark the agentive grammatical role of a noun in a sentence. Although certain nouns do have a permanent trait of agency (agent noun: runner, kicker, etc.), an agent noun is not necessarily an agent of a sentence: "Jack kicked the runner".

The notion of agency is easy to grasp intuitively but notoriously difficult to define: typical qualities that a grammatical agent often has are that it has volition, is sentient or perceives, causes a change of state, or moves. The linguist David Dowty included these qualities in his definition of a Proto-Agent, and proposed that the nominal with the most elements of the Proto-Agent and the fewest elements of the Proto-Patient tends to be treated as the agent in a sentence. This solves problems that most semanticists have with deciding on the number and quality of thematic roles. For example, in the sentence His energy surprised everyone, His energy is the agent, even though it does not have most of the typical agent-like qualities such as perception, movement, or volition. Even Dowty's solution fails for verbs expressing relationships in time:

...
Wikipedia