In this article, we address the question of phraseological innovation. By this, we refer to any new expression which does not constitute a regular collocation (a known expression) within a given language. Our objective is not to propose a theory of stylistic creativity. Instead, we limit our investigation to explaining how an expression comes to be integrated in the lexicogrammar as defined by M. A. K. Halliday. We also discuss various issues of terminology, notably the oppositions collocation/colligation, synthème/phrasème which have currently come to the fore in the fields of lexicography and French functional linguistics. These terms do not in fact help us to deal with the problem of phraseological innovation. So we turn instead to the semiotic notion of denomination, defined as the potential for a sign to refer globally within a given discourse. This approach avoids the traditional debate about whether expressions are syntactically fixed or semantically opaque. Rather, the main defining criterion which is of interest to us is the moment when a construction becomes independent of the discourse in which it is formulated in order to be assimilated as an expression by the speech community. As a case in point, we examine the emergence of a new expression in an extract from Trainspotting by Irine Welsh.