The paper investigates the semantic area of Epistemic Modality in Modern Greek, by means of a corpus-based research. A comparative, quantitative study was performed between written corpora (informal letter-writing) of non-native informants with various language backgrounds and Greek native speakers. A number of epistemic markers were selected for further qualitative investigation on the grounds of their high frequency. The qualitative study revealed the ways epistemic markers (grammatical and lexical) are used in order to express the speaker's stance while they perform a number of discourse-pragmatic functions without violating the societal norms of politeness. The present study made use of the literature on Epistemic Modality, the face-management theory of politeness and the interpersonal metadiscoursal features known as hedges and boosters.