While the so-called “nominative-and-infinitive” (NCI) is no longer a productive construction in Dutch, the grammar of Present-day Dutch still contains a small set of lexically substantive NCI patterns, most notably geacht worden te and verondersteld worden te. Like their English formal equivalent be supposed to, these Dutch patterns can instantiate both evidential and deontic constructions, the latter being the most frequent one in Dutch. This paper focuses on the history of these deontic uses. We show that, with both patterns, the deontic use did not really take off until well into the second half of the 20th century and argue against an analysis in terms of grammaticalization along an (unlikely) ‘evidential to deontic’ path. Instead we present a language-contact hypothesis which attributes the development of the deontic uses of Dutch geacht worden te and verondersteld worden te to polysemy copying or distributional assimilation, English be supposed to providing the model. Additional evidence for the influence of English on this domain of Dutch grammar comes from the newly emerging lexically substantive NCI pattern verwacht worden te ‘be expected to’.