The central problem of this paper is the evolution of common nouns assumed to have turned into indefinite pronouns. The linguistic data have been retrieved from the Costuma d’Agen, a 13th-century Occitan Customary. The choice of this text is warranted by multiple relations obtaining between the architecture of legal codices and the presence of indefinite expressions. In this text, the contexts in which re (< Lat. acc. rem), ‘anything’ or ‘nothing’ occurs have been identified. This word is shown to be pervasive in Negative Concord (NC; under the scope of no(n), the expression of clausal negation), thereby meeting the requirements imposed upon negative polarity items (NPIs). Outside NC, re appears in conditional protases and temporal clauses introduced by ‘before’. Irrespective of the context in which it appears, Old Occitan re turns out to be fairly advanced on the grammaticalization scale: unlike its etymon, it no longer inflects for number, it does not take determiners and fails to function as a subject in the Costuma d’Agen. Comparative evidence from Gascon 13th century texts proves that, although the descendants of rem of that period occur in the same structural environments (all of them are, by then, free-choice items, FCIs), they do not evolve at the same pace as their Occitan cognate. In other words, even in neighboring linguistic zones, these expressions differ with respect to the degree of persistence of syntactic properties inherent to Latin common nouns. Finally, re is matched against other FCIs, such as hom or home ‘anybody’ or ‘nobody’ and autrui ‘someone else’ or ‘someone else’s’. Compared to re, the medieval developments of these items are far more diversified and retain more original features of their etymons. The difference is traced back to the greater conceptual salience of the animate domain.