Mexican Spanish is often described as a conservative variety whose distinguishing features go back only to the 19th century. This dissertation proposes that the origins of Mexican Spanish, at least with regard to verbal paradigm reduction, may be traced to the first century of the colonial period. My analysis is based on the collection of documents compiled in Documentos linguisticos de la Nueva Espana: Altiplano Central by Concepcion Company. The documents in this book are non-literary sources written during the colonial period. The following subjects were studied in this dissertation: language policy and Castilianization during the colonial period in Mexico, forms of address and the elimination of the second person plural, the -ra form and its function as an imperfect subjunctive and, finally, a historical analysis of the temporal values of the present perfect. It was found that the Mexican Spanish verbal paradigm, since the first century of the colonial period, has been characterized by the reduction of plural forms and a tendency to prefer the ending -ra form for past subjunctive, and a temporal value of an open past for the present perfect. However, there were two specific periods of time when this tendency was broken, at the beginning of the 17th and of the 19th century. At the same time, these two periods were characterized by a reassessment of the European values and imposition of its linguistic norms. This study confirms that, during the colonial period Mexican Spanish was caught between two strong opposing tendencies. One of these tendencies is the process of linguistic simplification, common in colonial territories; and the other is the process of monocentric standardization, by means of which the linguistic norm of Spain exerted pressure in the colonies.