It has frequently been noted that non-native speakers of English find it difficult to express their views with the appropriate degree of conviction. However, many of the problems which non-native speakers have with specific modal expressions are still waiting to be identified. The aim of this paper is to compare native and non-native (student) uses of two English epistemics: "surely" and "for sure". The students' uses are mostly examined with reference to PICLE (the Polish subsection of the International Corpus of Learner English), while native uses are analyzed on the basis of two corpora of texts written by native speakers of English available at the PICLE website, the British National Corpus, and scholarly publications concerning the two particles. The study demonstrates that Polish students tend to wrongly assume the functions of surely and for sure to be identical with the functions of the Polish expression "na pewno" (a literal equivalent of "for sure" with a broader range of uses). In consequence, they use the challenging and pressure-building particle "surely" in contexts which require neutral epistemic adverbs, such as "clearly". They also tend to put "for sure" in positions characteristic of epistemic adverbs, and use it in formal discourse.
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