Semantically, each event involves participants and non-participants. The former are the roles necessitated by the predication itself, and the latter are optional roles required by the semantic context. Participants answer the question of ‘who did what to whom’, non-participants answer the question of ‘why, where, when and how’. For example: ‘Lǐ Sì zài fàntīng lǐ pāi qiú’ (Li Si is hitting a ball in the dining-room). The predicate ‘pāi’ (hit) takes three arguments: the logical doer ‘Lǐ Sì’ (Li Si), the logical receiver ‘qiú’ (the ball) and the location ‘fàntīng lǐ’ (in the dining-room). Among them, the logical doer and receiver are more essential to the predication than the location, because elimination of either the doer or the receiver the predication of ‘pāi’ (hit) cannot be realized, but if the location argument ‘fàntīng lǐ’ (the dining-room) is deleted, the predication ‘Lǐ Sì pāi qiú’ (Li Si hits the ball) still holds. Thus, the doer and the receiver have the roles of participants, while the location has the role of non-participant; it is selected by the semantic context, but not by the predication itself.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.