Agent (grammar)

In grammar, the agent is the thematic role (also known as a semantic role or theta role) assigned to the entity that intentionally performs the action described by the verb. The agent is typically a person or animal, but can also be an entity conceptualized as having the capacity to act intentionally.

The agent contrasts with other thematic roles, such as the patient (the entity that undergoes the action), the instrument (the object used to perform the action), and the experiencer (the entity that experiences a sensation or emotion).

Identifying the agent is crucial for understanding the meaning of a sentence and how the different elements relate to one another. In active voice constructions, the agent is often the subject of the sentence. However, in passive voice constructions, the agent may be demoted to a prepositional phrase introduced by "by" or even omitted entirely.

For example, in the sentence "The dog chased the ball," the dog is the agent because it intentionally performed the action of chasing. In the sentence "The ball was chased by the dog," the dog is still the agent, but its grammatical role is shifted in the passive construction.

The concept of agenthood is fundamental to many linguistic theories and is used in analyzing the structure and meaning of sentences across different languages.