This article combines methodologies from corpus linguistics with an experimental-like setup more affiliated to psycholinguistic research. The resulting methodology allows us to gain more insight into cognitive motivations of language use in speakers from the past, and consequently to better assess their similarity to present-day speakers (the Uniformitarian Principle). One such cognitive motivation thought to be relevant in the early stages of grammatical constructionalization (grammaticalization) is covered by the evasive concept of ‘extravagance’ (i.e. the desire to talk in such a way that one is noticed). The methodology is tested on the Early Modern English extension of the [be Ving]-construction to progressive uses in present-tense main clauses. It is argued, on the basis of recurrent contextual clues, that [be Ving] in this novel use is motivated by extravagance. Interestingly, a comparison of two speaker/writer generations that are among the earliest to use this innovation with some frequency suggests that the encoding of extravagance shifted between them. At first, extravagance was signalled by coercion of the still stative semantics of [be Ving] into a progressive reading. In the second generation it had become an entrenched characteristic of the construction itself.