accordingly, the verb "examine" must have a dp (determiner phrase) as an agent and a dp as a theme. however, in (3a), since no overt dp functions as the agent of "examine", this should be a violation of the theta criterion. however, the presence of the null pro subject, as shown (3b), satisfies the theta criterion by having pro as the dp in the sentence and "the patient" as the dp. the tree diagram (3) represents how pro satisfies the theta criterion of "examine" by being the dp in the non-finite clause.