Bloom et al. (1975a, b) and Brown (1973); the Danish and French examples, in (2) and (3) respectively, are from Hamann and Plunkett (1998).(1) a. Want more apple. b. Tickles me. c. No play matches. d. Show Mommy that. (2) a. Ikke kore traktor. Not drive tractor '(I, you, he) doesn't drive the tractor.' b. Se, blomster har. Look, flowers have. 'Look, (I, you, he, she, etc.) have/s flowers.' (3) a. A tout tout tout mangé has all all all eaten '(He) has eaten everything.' b. Oter tout ta. empty all that '(I) empty all that.'According to Hyams (1983Hyams ( , 1986, all children start out speaking 'Italian' with respect to the null subject option. The formulation of the pro-drop parameter I adopted was inspired by Rizzi (1982), who argued that in some languages (e.g. Italian, Spanish) Agr is essentially a subject pronoun making the overt expression of the subject DP optional; in other languages (e.g. English, French) Agr is not pronominal and null subjects are therefore not licensed. The particular parameter I suggested, as distinct from Rizzi's, clustered the null subject property together with several other properties of (early) grammar, including the lack of lexical expletives (e.g. in weather and raising constructions) and modals as a distinct verbal category. The developmental prediction of such a system was that children would show all the characteristics of the [+pronominal] Agr setting at the same time. And those children for whom the target is not a pro-drop grammar, for example English and German-speaking children, would lose all these properties at roughly the same time at the point at which the parameter was reset to a [−pronominal] Agr. Two developmental stages are therefore predicted with respect to null subjects (and other properties), Italian, then English (or German).This particular implementation of a developmental or "real time" parameter setting model turned out to be empirically flawed in a number of respects (which I return to below), but the logic seemed, and still seems to me to be correct. There are, in particular, three noteworthy features. First, the parameter setting model provides a narrowly constrained, and hence more explanatory model of acquisition than earlier standard theory, rule-based models. The "rules" of early grammar and the "errors" that children make are not random, nor do they arise from principles not