Epistemic modality is concerned with the speaker's attitude to the truth value of a proposition. With epistemic modality, speakers express their judgements about the factual status of a proposition. (see F.R. Palmer. Mood and Modality. 2nd edition. Cambridge: University Press 2001, p.8)
Epistemic modality is often expressed by adverbs like certainly, probably or perhaps, but it may also be expressed by modal verbs or, as in some Creole languages, by TAM markers.