In addition, the speaker may put the focus upon a particular part of the statement; then the adverbial has the function of restriction:
Tā zhǐ duì gōngzuò rènzhēn.
(He has been conscientious only about his work.)
Zhǐyǒu tā duì gōngzuò rènzhēn.
(Only he has been conscientious about his work.)
In (1a), his quality of ‘being conscientious’ is true only to his work, but not true, for instance, to matters about his family or friends, etc. The limit application of the predicate is due to the presence of the focusing adverbial ‘zhǐ’ (only). As shown by the examples, the adverbials expressing the information of modality reflects the speaker’s subjective attitudes and orientations toward the content of a statement, though they may be objective measures of factual status of the statements.
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.