Modern Greek clitic pronouns and the ‘surface structure constraints’ hypothesis

In his (1970) article ‘Surface structure constraints in syntax’ Perimutter has argued that the restrictions on the combination of the weak atonic forms of the object pronouns in Spanish and restrictions on their order cannot be accounted for naturally either in the deep structure, by constraints on the phrase structure rules, or by constraints on the rules which introduce these pronouns.1 He concludes that a transformational generative grammar must be supplemented by positive output constraints which act as a filter accepting only sequences which match the filter and rejecting the rest as ungrammatical.