Low-certainty modals not future tenses cause increased psychological discounting

Speaking a language that obliges the future tense for linguistic Future Time Reference (FTR) has been hypothesised to cause speakers to perceive delayed outcomes as temporally distal and therefore less valuable (“temporal discounting”). Conversely, we hypothesise that the obligation to use low-certainty modal verbs, e.g. may, causes speakers to construe risky and delayed outcomes as riskier and therefore less valuable (“combined discounting”). We experimentally elicited free-text FTR responses and measured construals of future temporal distance and discounting of (risky) delayed rewards in speakers of Dutch (which does not oblige FTR marking) and English (which does). We used statistical mediation models, which parse out an indirect effect of a predictor on an outcome via a mediating variable, a direct effect of a predictor on an outcome, and a total effect—the other two combined. English speakers construed future events as temporally proximal, which in turn caused less (rather than more) temporal discounting (indirect effect). The direct effect went in the opposite direction, meaning there was no population-level difference in temporal discounting (no total effect, Study 1). When we measured combined discounting, English speakers discounted more (a total effect, Study 2). Further, English speakers used more low-certainty language and this caused increased combined discounting (an indirect effect). Future tense use did not impact construals of temporal distance, meaning future tense use did not mediate an effect on combined discounting (Study 2). We addressed possible cultural confounds by testing Dutch-English bilinguals (Study 3). When bilinguals were tested in English, they used more low-certainty modal verbs, which in turn caused increased combined discounting (an indirect effect). This was moderated by self-reported English proficiency, indicating language, not culture, is responsible for effects. Results suggest effects of FTR grammar are not driven by obligatory future tenses affecting temporal discounting, but by obligatory low-certainty modals affecting combined discounting.