The preposition ‘zai’, derived from the verb ‘zai’, has the basic meaning of ‘exist in space’. Thus the adverbial of position ‘zai + NPloc’ phrase denotes the location where the subject referent executes an action. According to Chinese conceptual structures, the subject referent must be physically present at the location before he performs the action named by the verb. Being present at a place expresses a state, which obtains before the subject referent’s executing the action. Hence the adverbial of position is placed before the verb in terms of the PTS. This rule is conventionalized, so even when the locative phrase indicates the location where an action takes place, instead of the physical presence of the subject, it is still placed before the verb, as shown by example (1d). Verbs in (2) are stative verbs, more specifically, they are posture verbs that depict the posture of the subject referent (which is typically an animate being). With posture verbs, the ‘zai’ phrase may occur both preverbally and postverbally, because there is no difference between naming the general location where the stative event (namely assuming a certain posture) occurs and naming the place where the subject referent ends up in that posture.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.