Adverbials can be used to express modality. We will introduce the reader to the notion of modality by an example sentence. Please consider: ‘He is a famous writer’, this is a straightforward positive assertion of the fact. But the speaker can qualify his statement with respect to the factual status of the information, like: ‘He seems to be/is probably a famous writer’. Though the sentence is not negative or counterfactual, it is contingent, and the assertiveness of the sentence is attenuated. The area of semantics that is concerned with the factual status of statements is defined as modality. Modality signals the relative actuality, validity or believability of the content of an expression, it is associated with the speaker’s attitude or opinion about what is said. It could be an objective measure of factual status, but it could also be a subjective attitude or comments on the content of a sentence (Frawley, 1994: 384).
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.