Adverbials are complex due to the following reasons: first, they have a wide range of semantic roles; second, they have distinctive grammatical functions (adjuncts, subjuncts, disjuncts, conjuncts); third, they may be realized by different forms (an adverb, a prepositional phrase, a NP, or a VP); fourth, there may be multiple occurrences of adverbials in a sentence; and last, their position is relatively flexible (occurring medially, initially or finally for highlighting the information).
[1] Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.
