The basic word order in Chinese is SVO (Li & Thompson, 1981; Chu, 1997). As pointed out by Greenberg (1966), in declarative sentences with normal subjects and objects, the dominant order is almost always one in which the subject precedes the object. It is not arbitrary or accidental that subject precedes object. According to Comrie (1989), ‘The grammatical role of subject is the intersection of Agent and topic’. Topic entails definiteness, that is, for an expression to be topic, the referent to which it refers must be definite, or identifiable in the context. A definite or identifiable entity has high referentiality. Cross linguistically, it has been observed that there is a natural correlation between Agent and animacy, that is to say, Agent is typically animate or human, and agency is connected with volition, will and responsibility. Agents deliberately, intentionally, responsibly execute and control an action or event; they generate effects, while they themselves are relatively independent of the action. The implication of the independent status of Agents as the source of an event is that they are seldom affected by the event, so they tend to be stable (Frawley, 1992). Since subject tends to be definite in reference and stable in nature, in accordance with the Principle of Referential Precedence (The Principle states that the human cognitive system favors beginning an utterance or a sentence with a linguistic unit of high referentiality), subject occurs in the initial position of a sentence.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.