In linguistics, a grammatical patient, also called the target or undergoer, is the participant of a situation upon whom an action is carried out. A patient as differentiated from a theme must undergo a change in state. A theme is denoted by a stative verb, where a patient is denoted by a dynamic verb. At the very least, there is debate to this effect. Also, patient is the name of the thematic relation with the above definition.
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 ate the cheese", "the cheese" is the patient. In certain languages, the patient is declined for case or otherwise marked to indicate its grammatical role. In Japanese, for instance, the patient is typically affixed with -o (the hiragana を). Although Modern English does not mark grammatical role, patienthood is represented irregularly in other ways; for instance, with the morphemes "-en", "-ed", or "-ee", as in "eaten", "used", or "payee".
The grammatical patient is often confused with the direct object. However, there is a significant difference. The former is based explicitly on its relationship to the verb, whereas the latter is based primarily on its relationship to the subject. For example, in the phrase "The dog bites the man", the man is both the patient and the direct object. By contrast, in the phrase "The man is bitten by the dog", the man is still the patient, but now stands as the phrase's subject; while the dog is only the agent. The term "theme" is often used to describe the same relation as patient.