This manuscript summarizes the history and experimental studies of a research project focused on the empirical testing of some of the assumptions that characterize the taxonomic proposal of Ribes and López (1985); specifically, those related to the progressive complexity and inclusiveness of the behavioral functions recognized by these authors. It was considered that behavioral adjustment should be quantified differentially depending on the complexity of the contingencies that give rise to one or another functional type of behavior, but similarly among them if the quantification focused on measuring a function X-1 included within a function X or X+1. It was expected that: a) the different adjustment indices would follow developmental rhythms and reach terminal states inversely proportional to the complexity of the behavior they supposedly quantify; and b) the same adjustment index would progressively decrease among increasingly complex functions. The results showed that both “hypotheses” were correct in the case of intrasituational functions.