In this work in the context of the variationist functional theory that links form, motivation and culture, we intend to show how the 19th century speaker in San Juan, Argentina, alternates in his family charters synthetic and periphastic language forms to refer to the future, according to his communication purposes. The corpus, made up of letters written between 1837 and 1889, is part of the ‘century of political independence and creations of the new states, in which the fight for identity in Latin America begins’ [Majfud, 2002]. We consider that alternating constructions do not amount to syntactic, semantic or pragmatically, and are favoured by certain parameters, of which we analyse the one by which we believe that the ‘go to + infinity’ area was innovative. We adhere to the fact that “functional explanations of linguistic changes do not exclude but involve cultural explanations” [Coseriu, 1977]. This pragmatic approach to linguistic use requires a qualitative and quantitative analysis at the same time. “It will matter not only which structures the language contains, but also when they are used and, above all, how much is used when to which structure” [García, 1995]