The effects of modal value and imperative mood on self-predicted compliance to health guidance: the case of COVID-19

 Health messaging is effective if it achieves audience adherence to guidance. Through the lens of Systemic Functional Linguistics, we examine the expression of obligation in poster-based health campaigns (4 posters) employed during the COVID-19 pandemic in the UK by considering whether differences in grammatical mood and modality values impact on public compliance toward the message content. Effects of mood and modality variations are examined through a quantitative-cum-qualitative analysis of results from a representative survey (N = 1,089), which included closed questions on self-predicted compliance to health guidance and open questions on the respondents’ understanding of messaging. The quantitative results favour medium values of obligation (“should” vis-à-vis “must”) and directives in declarative mood for self-efficacy messages, and expressions of certainty when the need to take action to prevent negative outcomes is conveyed. The qualitative results show that, communication context and linguistic features being equal, message types (i.e., self-efficacy, moralising, fear appeals) and visual cues prevail in conditioning public reception. Moreover, since directives employing modality allow for speakers’ inclusion among the targeted addressees, they appear to offer more favourable outcomes than those in the imperative mood. This study provides empirical insights into the effects of modality and mood on health guidance compliance.