Abstract
This thesis compares how native speakers of English and Norwegian learners of English use the modal auxiliary MUST and the quasi-modal HAVE TO in order to express different types of modality. The data needed was gathered from the Louvain Corpus of Native English Essays, which contains essays by English students; and the Norwegian International Corpus of Learner English, which holds essays by Norwegian learners of English. The data was divided into the categories of root and epistemic modality. Epistemic modality expresses the speaker’s judgment of the truth of an utterance or notion. Root modality is an umbrella-term which includes permission, obligation, volition, and ability. Root modality was further divided into the categories of deontic modality, which comprises necessity borne of imposition; and dynamic modality, in which the necessity is rooted in circumstances. My analysis suggests that Norwegian learners generally tend to use HAVE TO more than MUST, whereas native speakers appear to use them more evenly. In terms of epistemic modality, both groups seem to prefer MUST over HAVE TO. As far as root modality is concerned, both groups tend to use MUST more frequently as deontic modals, and HAVE TO as dynamic modals.