We utilize variationist methodology to explore the conventionalization and pragmatics of 3rd person direct object clitic placement in Spanish periphrastic constructions. Analysis of 652 tokens extracted from three Mexico City speech corpora indicates that while proclitic position is the majority variant, the rate of enclitic position depends on particular [finite + non-finite verb] constructions, distinguished by frequency measures and more grammaticalized meanings. At the same time, enclisis is favored by propositional or non-referential direct objects and by direct objects of low topic persistence, measured by subsequent mentions. In contrast, proclitic position is favored more by inanimate than human referents, especially those that show topic persistence and whose previous mention was in the syntactic role of direct object in the same or preceding clause. These quantitative patterns suggest that proclisis indicates prototypical DOs in non-prototypical use, i.e. topical inanimates. Thus, despite conventionalization of the general proclitic schema, particular constructions and semantic-pragmatic considerations are operative factors in the variation.