Research on Montreal French (Laberge and Sankoff 1979; Thibault 1991) has shown a spectacular rise in the use of indefinite tu (or vous) in recent decades, at the expense of the standard form on. Although grammars of French have traditionally passed over indefinite tu/vous in silence, Ashby's study of Tours French (1992) confirmed that the phenomenon exists in metropolitan French also. The historical time-depth of indefinite tu/vous has apparently not been explored previously, though Posner (1997) has suggested that indefinite tu is a modern feature, found especially in Canada. A survey of indefinite tu/vous in earlier periods and in a range of varieties forms the first part of this paper. Secondly, drawing on a corpus of French spoken in Picardy, northern France, the paper investigates the extent to which this use of the 2nd person pronouns: (i) helps to avoid ambiguity; (ii) co-occurs with another grammatical variable. Unlike the surveys of Montreal and Tours, the Picardy corpus includes a large majority of informants who used tu to address the interviewer, and this too is explored as a potential influence on speakers’ use of 2nd person pronouns with indefinite reference.