The middle ground between these two extreme cases can be indicated by adverbials expressing approximate ideas, which may take various guises:
Tā gōngzuò dàgai/kěnéng rènzhēn.
(He has probably been conscientious about his work.)
Tā gōngzuò bú zhēnde rènzhēn.
(He has not really been conscientious about his work.)
Tā gōngzuò jǐhū bú rènzhēn.
(He has hardly been conscientious about his work.)
Obviously, the truth value of the statement ‘He works conscientiously’ is attenuated or varnished by the adverbials ‘dàgai/kěnéng/bú zhēnde/jǐhū’ (probably, possibly, not really, hardly).
 Loar, J. K. (2011). Chinese syntactic grammar: functional and conceptual principles. New York: Peter Lang.