Grammatical roles such as subject, object and verb belong to the domain of syntax, they are features of sentences. For example, subject is a relation between a noun and a verb such that the noun typically determines the singular or plural form of the verb (as in English). The standard view on grammatical roles in functionalism is that they are phenomena of an intermediate level between semantic and pragmatic roles, and they are the formal coding of both semantic and pragmatic relations (Andrew 1985). Semantic roles and pragmatic roles are two logically independent notions, but there is a strong correlation between the two notions in practical communication. Some semantic roles are readily and frequently taken as topic, while others as the focus, as observed by Comrie: “Other things being equal, one would expect agent and topic to coincide” (Comrie 1989:120). Likewise, the semantic role of Patient, which signifies a change of state, readily becomes new information or focus. Grammatical roles may capture this correlation and encode topic and Agent as subject, and encode Patient as object. Hence in the literature, it has been observed that the grammatical role subject is the intersection of Agent and topic, and the object the intersection of Patient and affectedness. Affectedness signals new information and focus, so it is suitable for the Patient to occur as the object which follows the subject and verbs to be the end-focus.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.