This paper tests two claims about the thematic roles Agent and Patient: first, that they can be decomposed into more primitive features, as laid out in Dowty's (1991) Proto-Roles Hypothesis; and second, that these properties can be inferred directly from the grammatical roles subject and object. In Experiments 1 and 2, participants rated the Proto-Roles properties of the subject and object of transitive sentences with real verbs. Subjects were rated as more Agent-like than objects, while objects were rated as more Patient-like than subjects. Experiment 3 used transitive sentences with nonsense content words (e.g. "The rom mecked the zarg"). Even in the absence of a known verb, the results were the same. Experiment 4 examined the corollary prediction that subjects and objects should not differ on grammatically irrelevant properties (e.g. "being liquid"); this prediction was confirmed. In Experiment 5, verbs that do not permit objects (e.g. "fall," "erupt") were placed in the transitive frame. Results were the same as in Experiments 1 through 3. Moreover, the semantics of the verb were altered by the frame, indicating that participants tried to fuse the semantics of the verb with those of the frame. Possible sources of these inferences are considered.