Between 1970 and 1980, due to economization process of extra economic field of human existence and an exclusively economic understanding of rationality, Sen realized a reversal compared to this tendency, thanks to the critical exchange with his contemporaries, as Arrow, Rawls and Harsanyi, about assumptions concerning individual preferences/collective choices, inequalities, rationality and social welfare functions. Here, I have considered this period as the foundational decade to capability approach: this analysis is fundamental not only for showing the intellectual origin of this approach, but also for avoiding dangerous trivializations which hinders a proper understanding of it.