<span style="font-size: 12.0pt; font-family: "Times New Roman"; mso-ansi-language: EN-US;">In this paper, we present empirical evidence showing </span><span style="font-size: 12.0pt; font-family: "Times New Roman"; color: black; mso-ansi-language: EN-US;">that</span><span style="font-size: 12.0pt; font-family: "Times New Roman"; mso-ansi-language: EN-US;"> Differential Object Marking (DOM)<span style="mso-spacerun: yes;"> </span>in Spanish is determined by structural conditions related to Case and agreement. We also argue that semantic concepts </span><span style="font-size: 12.0pt; font-family: "Times New Roman"; color: black; mso-ansi-language: EN-US;">such as specificity, definiteness, animacy, or topicality, tightly connected to the presence or absence of <em style="mso-bidi-font-style: normal;"><span style="font-variant: small-caps;">A</span>, </em></span><span style="font-size: 12.0pt; font-family: "Times New Roman"; mso-ansi-language: EN-US;">must be parasitic on the syntactic configurations where DOM is licensed.</span><span style="font-size: 12.0pt; font-family: "Times New Roman"; color: red; mso-ansi-language: EN-US;"> </span><span style="font-size: 12.0pt; font-family: "Times New Roman"; mso-ansi-language: EN-US;">We also present some consequences of our analysis for the general theory of agreement. We argue that the same structural relation is involved in all cases of DOM, as well as in Dative Clitic Constructions, where the</span><span style="font-size: 12.0pt; font-family: "Times New Roman"; color: black; mso-ansi-language: EN-US;"> presence of the particle<em style="mso-bidi-font-style: normal;"> A</em> preceding clitic-doubled </span><span style="font-size: 12.0pt; font-family: "Times New Roman"; color: windowtext; mso-ansi-language: EN-US;">datives is syntactically unified with DOM phenomena. The accusative/dative distinction traditionally attributed to the Spanish pronominal system does not correspond, in synchronic terms, to different case relations, but distinguishes between agreeing and non-agreeing arguments. Similarly, the distribution of DOM corresponds to a Case-checked/Caseless difference. We extend the analysis to account for well-known restrictions on the co-appearance of two DOM</span><span style="font-size: 12.0pt; font-family: "Times New Roman"; mso-ansi-language: EN-US;"> arguments, which <span style="mso-spacerun: yes;"> </span>are analyzed as the consequence of a competition between two arguments for a single target. <br /></span>