Spanish allows clitics to appear in one of the two positions in ‘VFIN + VINF’ structure: either before the matrix verb or behind the embedded verb. Previous analyses account for this in terms of clause reduction/restructuring(Contreras 1979, Rizzi 1982) or Equi-NP deletion(Quicoli 1976). However, they do not answer two crucial questions: (i) why does the clitic undergo an obligatory promotion when clause reduction applies?; (ii) why does the proclitic appear morphologically separated from the verb and why does the enclitic appear morphologically integrated to it?. In this paper, we try to answer these questions based on the LCA(Kayne 1994). Following Postal(1966) we assume that clitic pronouns are bare Ds without complements and point out that the embedded verb and the clitic mutually c-command in ‘VFIN + VINF’ structure and so no ordering is assigned to them. We claim that Spanish provides two ways of circumventing this problem. One is to move the clitic to a higher position. This is the reason why the clitic is promoted to the matrix clause. The other is to form a complex verb through a morphological reanalysis between them. The morphological integration between them is a reflex of the complex head formation. Finally, to account for why the proclitic appears separated from the verb we assume that the clitic moves to the head of Clitic Phrase and that its integration with the verb takes place later, probably at PF. Under these assumptions we claim that the morphological integration at PF is “less strong” than at the morphological component and so the morphological separation between them is a reflex of the less strong integration.