In addition to a grammatical PATIENT and AGENT, Umu sentences also includes the element of TOPIC.
The TOPIC of a sentence is what the sentence is about. It always comes last in the sentence. For example:
The topic can always optionally be set apart from the rest of the sentence with a pause. Topics need not be overt.
Topics need not have a direct semantic relationship with the verb; patients and agents must.
The concept of TOPIC is crucial in explaining the structure of ordinary sentences. The concept of SUBJECT not grammatically defined. In ordinary conversation, it may be missing altogether.