Low-certainty modals not future tenses cause increased psychological discounting in English relative to Dutch

Speaking a language that obliges the future tense for linguistic Future Time Reference (FTR) may cause speakers to devalue future outcomes. Evidence suggests such grammars make speakers less "future-oriented": less likely, for example, to invest, eat healthily, or support costly climate change mitigation efforts. This has been explained using the notion that the future tense (e.g., will) encodes temporal notions of distance and/or precision; its obligatory use is therefore hypothesized to cause speakers to perceive delayed outcomes as less valuable. We argue that this causal account is not supported by extant evidence. Rather, we hypothesize the obligation to use low-certainty modal verbs (e.g., may) causes speakers to construe delayed outcomes as risky and therefore less valuable. We tested this in speakers of Dutch (which does not oblige FTR marking) and English (which does). English speakers used more low-certainty modal verbs, which in turn caused them to place a relatively lower value on future outcomes; at the same time, future tense had no effect, in terms of either distance or precision, on reward value construals (Study 1). When bilinguals were tested in English and Dutch, increased relative use of low-certainty modals again caused English speakers to devalue future outcomes, addressing possible cultural confounds (Study 2). English and Dutch speakers were tested on a non-linguistic probability estimation task; higher modal verb use in English caused lower probability estimates relative to Dutch speakers on matched visual stimuli-supporting the modal account that the obligation to use low-certainty language impacts judgments about probability (Study 3). Relative to matched US nationals, corporate executives from countries which speak languages that, like Dutch, do not oblige future statements to be grammatically marked, used fewer low-certainty modal verbs and more present tense FTR statements, while there was no difference in future tense use (Study 4)-broadly supporting the modal account by suggesting the modal differences characteristic of English and Dutch are widespread. Together, these results indicate that, relative to Dutch, English FTR requires speakers to use more low-certainty modals, and that this negatively biases construals of probability, which in turn leads to increased discounting (Studies 1-3), and that this cross-linguistic contrast may be general (Study 4). The studies provide evidence for linguistic relativity by identifying cross-linguistic effects of FTR grammar on discounting via low-certainty modals. However, the hypothesis that obligatory tenses impacted discounting via temporal notions was not supported, suggesting numerous reported results should be re-evaluated using the causal framework we propose.