This dissertation focuses on the apparent linguistic discontinuity reflected in notarial texts from the twelfth to the thirteenth century in the Iberian Peninsula. Particular attention is given to the historical development of Spanish personal a (the direct object animacy marker), which can be used to trace the communicative continuity that must have bound the speakers of these chronologically adjacent centuries in spite of the multiple orthographical differences exhibited by the documents of this time period. In this discussion, I compare and contrast Menendez Pidal's (1926/1950) theory--which characterizes High Medieval Spain as a diglossic community--with Roger Wright's (1982, 2002) opposing views. Following Wright's (1982, 2002) "complex monolingualism hypothesis" and Koch y Oesterreicher's (2007) notion of the "sociolinguistic continuum", I combine evidence supplied by Early Romance documents dating from the ninth through the thirteenth century with evidence drawn from reformed spellings found in the Castilian texts composed after the latter century. The aim of this investigation is to trace the diachronic evolution of the Spanish personal a from its origins. In the first phase of this study, I present the morphophonological and syntactic traits shared by notarial texts composed in the Spanish High Middle Ages. In the next section, I compile the earliest personal a attestations (many of which date back to the eleventh century) and illustrate how these early attestations are complemented with eight new examples of this morphosyntactic phenomenon coming from the "Diplomatic Collection of the Monastery of Sahagun" (Herrero de la Fuente 1988). Finally, I offer a syntactical-semantic account of the distribution of the personal a in the Late Medieval period. The presence of the accusative a in documents composed before the thirteenth century allows me to claim that: (1) the Spanish accusative a has its primitive origins before the appearance of phonetically-based Castilian writing in the thirteenth century, (2) Spanish a unites Late Latin and Early Hispano-Romance, and (3) this animacy marker provides evidence for a sociolinguistic continuum that encompasses the High Middle Ages. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]