From Must to Have to: Frequency Changes in the Modal and Semi-modal in Contemporary English

Abstract

This thesis examines the frequency changes of the modal verb must and the semi-modal construction have to in contemporary English. In addition to examining frequency changes, this study aims to find evidence of a pattern of internal obligation being used in association with the modal must and external obligation being used in association with the semi-modal have to. Modal verbs are auxiliary verbs used to indicate modality, which refers to the speaker’s attitude towards a proposition. This study focuses on deontic modality expressing obligation. In addition to core modal verbs, such as can, must and should, semi-modal constructions, such as need to, have to, ought to, are also used to express modality. These semi-modals act as modals but function as main verbs.

The data for this study was collected from the News on the Web corpus. Two separate subcorpora were created for the data collection, one for the year 2010 and one for 2025. This allows for examination of diachronic change in news texts published 15 years apart. Both virtual corpora include 8000 news texts published in Great Britain. The search queries are limited to first person singular and search for any verb following must or have to. The frequencies are then analyzed and compared numerically. The retrieved tokens are analyzed manually to determine whether they depict internal or external obligation.

The results show evidence of the semi-modal have to being the more common form in denoting obligation over the modal must. The frequency of both must and have to declined between 2010 and 2025. Nevertheless, have to gained prominence over must by being 6.67 times as frequent in the 2025 corpus whereas it was only 3.27 times more frequent in the 2010 corpus. There was also clear evidence in the results to support the claim that must is most often used to denote internal obligation and have to external obligation.