AbstractThis study revisits variable subject pronoun expression in Spanish, bringing to bear insights from cross-linguistic patterns of person-number systems. Based on 2259 tokens from two corpora of Mexican Spanish representing distinct social classes, the study focuses solely on first person plural (1pl) subject pronouns, revealing unique aspects of variablenosotrosexpression. Evidence is offered in favor of a more nuanced measure of switch reference for non-singular grammatical persons through an analysis of the local effects of partial co-referentiality. This measure reconciles the large body of work on switch reference with Cameron’s (1995) measures of reference chains. Additionally, topic persistence — heretofore neglected in prior studies — conditions the variation, with subsequent mentions in the thematic paragraph favoring expressed pronouns. An investigation of clusivity demonstrates that Spanish 1pl subject pronoun expression is sensitive to a distinction grammaticalized in other languages, though subject pronoun rates across clusivities differ from previous results from Peninsular Spanish (Posio 2012). Finally, while subject pronoun expression is generally not sensitive to social factors, distributions of 1pl subjects according to clusivity differ between corpora. Results reveal the style and topic-conditioned differences in contextual distributions that underlie apparent social class differences in subject expression constraints.