In some Spanish dialects, direct object arguments of transitive clauses under certain conditions allow co-occurrence of a pronominal clitic with a coindexed lexical NP (direct object clitic doubling). In Limeno, as well as in Standard Spanish, in accordance with Kayne's Generalization, direct object clitic doubling obtains only under a-marking, by conveying animacy and specificity on direct objects. This paper explores the motivations and mechanisms of a-marking based on these referential categories with an emphasis on optional marking. It focuses on the resulting morphosyntactic reflexes: mood in relative clause, a-marking DOM, and clitic doubling. This analysis links Kayne's Generalization to topic marking in Spanish, which mostly seems to hold, by associating the semantic feature specificity with the discourse roles TOP and FOC. The evolution of clitics from marking agreement to marking a secondary topic is ascribed to a known grammaticalization process of the formative a.