The point of departure for the claims I wish to make in this chapter is the general assumption that one cannot escape if one takes seriously Vygotsky’s (1987) insights on the co-development of language and thinking and Wittgenstein’s (1953) criticism of the thinking-language dichotomy: Human thinking is the individualised form of interpersonal communication, and the way we communicate with others and with ourselves has therefore a major impact on how we act and how we perceive the world (Sfard, 2007b, 2008; cf. Edwards & Potter, 1992; Harré & Gillett, 1995). Various types of communication, or simply discourses, differ from one another in their vocabularies and word use, in their mediators and routines, and in

the narratives they produce. In particular, participants of each discourse have their own ways of constructing, defending, and eventually endorsing stories about the world. Among the most prominent and infl uential of these narratives are those we call identities-stories about who we are, with whom we belong, and what position we occupy among those who constitute our human environment. When discourses change, the whole world changes, and our identities change with it. In particular, the human world described in terms of numbers is defi nitely not the same as the world described in number-free language.