The development of grammatical markers has been described from several theoretical perspectives over the last decade: Grammaticalization Theory (Hopper & Traugott 2003, Heine, Claudi & Hunnemeyer (1991), the Minimalist Program (Roberts & Roussou 2003, van Gelderen 2004), and Lexical-Functional Grammar (Vincent 2001), see also the overview in (Borjars & Vincent 2010). It has recently been addressed in Construction Grammar, where it is argued that a shift towards a constructional perspective on change may yield new insights into the workings of grammaticalization (Bergs & Diewald 2008, Hoffmann & Trousdale 2013, Traugott & Trousdale 2013). This paper should be taken as a contribution to a constructional view on grammaticalization. It is about the rise of the concessive subordinator fast(än) in the history of Swedish occurring in a construction or clause type called UNIVERSAL CONCESSIVE CONDITIONAL (Haspelmath & Köning 1998), in Swedish GENERALISERANDE BISATS (SAG 1999). The Swedish fast , etymologically (and still productively) as an adjective in the meaning ‘steady’, ‘robust’ is used as an intensifier,‘very’, ‘much’, in early Modern Swedish, eventually established as a concessive marker ‘even if’, ‘although’ in the 18th century. The conventionalization of a concessive inference is highly interesting and may be traced back to specific constructions in the 16th and 17th centuries. On the basis of an extensive corpus study, I analyze the critical contexts and discuss the development as constructional change rather than lexical change, arguing that a remapping between form and function takes place in concessive conditional constructions due to processes of inferencing and mismatch.