Køppe's proposition of four layers in theoretical building are used here in the exploration of a specific case of eclectic combination, the use of Piagetian and Vygotskian general approaches to the analysis of proportional reasoning as a cognitive mathematical ability. It is proposed here that the eclectic consideration of these contributions depends on the consideration of their specificity, in the sense that they highlight different aspects of the phenomenon under scrutiny, and also on the consideration of the coherence between this eclectic convergence and premises in terms of schools of thought under which each contribution is framed. We conclude proposing in accordance to S. Køppe's proposal that eclecticism can be valuable and heuristic in theory development, but this contribution will depend largely on the effort in establishing careful relations between the four layers of theory-building.