How preschoolers acquire the null-overt contrast in Mexican Spanish

In many so-called true null subject languages, null and overt subject pronouns have contrasting referential preferences: null subjects tend to maintain reference to the preceding subject while overt pronominal subjects do not. We propose that children acquire this contrast by initially restricting their attention to 1st and 2nd person pronouns, whose intended referents are simpler to infer. Production data from Mexican Spanish shows that (i) the null/overt contrast is in principle acquirable from 1st and 2nd person subject pronouns in naturalistic input, (ii) children’s production of 1st and 2nd person subjects is conditioned by this contrast early in life (approximately 4½), and (iii) the contrast is generalized to the 3rd person slightly later (by 6).