As for the functions played by adverbials of expressing the information about modality, McCawley (1978) suggests that ‘The adverb is world-creating, that is, it sets up a belief context, or a possible world, against which the content of a proposition has to be judged’. As shown:
Mǎ Lì zhǎodào le yífèn mǎnyì de gōngzuò.
(Ma Li has found a satisfactory job.)
Mǎ Lì sìhū zhǎodào le yífèn mǎnyì de gōngzuò.
(Ma Li seems to have found a satisfactory job.)
Compare sentence (1a) with (1b).The proposition expressed by sentence (1a) is that ‘Ma Li found a satisfactory job’. In (1b), the addition of the adverbial ‘sìhū’ (it seems, seemingly) lessens the truth value of the sentence. If paraphrased, the sentence means: ‘I tentatively assert that Ma Li has found a satisfactory job’. Obviously, the truth value of the proposition is judged against the adverbial ‘sìhū’, which attenuates or varnishes the factual status of the proposition. This restriction on the factual status of the statement is entirely due to the function of the adverbial ‘sìhū’ (apparently, seemingly), because if we take out the adverbial as in (1a), the statement is quite determinate. Thus the adverbial ‘apparently/seemingly’ signals the speaker’s attitude or state of knowledge about the proposition.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.