"This paper is an attempt, primarily, to formalize the model of "reconstruction of the logic of development" of "social formations" summed up by Habermas through the differentiation between vital world and social systems (and, within them, through the "rationalization of the world of life" and the "growth in complexity of the social systems").Secondly, it tries to offer some methodological clarifications about the "explanation of the dynamics" of "historical processes" and, in particular, about the "theoretical meaning" of the evolutional theory's propositions.