Abstract
This work provides a case study centered on the cognitive phenomenon of factualization, viz. "the SP/W's increasing certainty about the realization of an event or situation" (cf. Tantucci 2014, 2015a, b, 2016b). Factualization corresponds to a cognitive-control mechanism (i.e. Kan et al. 2013) specifically occurring in the epistemic domain. It instantiates both in online language production and throughout the diachronic reanalysis of a construction (i.e. grammaticalization, semasiological change or constructionalization, cf. Traugott and Dasher 2002; Traugott and Trousdale 2013). The case presented here focuses on the diachronic change of the epistemic construction I suppose in British English. It will be shown that I suppose developed through time an increasingly factual usage out of an original meaning conveying weak epistemicity. Qualitative and quantitative data from the Corpus of Historical American English will support the general claim that-to varying degrees-epistemic predicates diachronically tend to develop new polysemies encoding a Speaker/writer's (henceforth SP/W) "subjectified form of certainty" towards a proposition P (cf. Tantucci 2015a: 371).