More on the clitic combination puzzle
Languages like Spanish, Catalan and Romanian accept combinations of 1st and 2nd person clitics. However, not all 1st and 2nd person combinations are possible. Although two single clitics can be combined, the combination of two plural clitics results in ungrammaticality (Rivero 2008; Nevins & Sãvescu 2008). This is true for Spanish and Romanian, but only partially for Catalan. On the other hand, all three languages accept clitic combinations that include a plural dative and a singular non dative and systematically reject combinations that include a singular dative and a plural non-dative. In view of this, I argue that there is a number-case restriction that parallels the Person Case Constraint, first proposed by Bonet (1991), and, in more general terms, I defend that clitic restrictions are drawn by the degree of markedness of the dative clitic with respect to the other clitic in the cluster.