Objective: We seek here to draw on the methods and tools put forward by Michel Foucault in The Order of the Things (1966) to shed light on history of welfare economics. More specifically we consider that the rejection of interpersonal comparisons that foreshadowed the marginalist revolution and the transition to ordinal measures of utility during the 19th century can be explained by the shift from the classical episteme to a modern episteme which is described by Foucault. Method: To explore this hypothesis, we drawn on the method of archaeological knowledge, proposed by Foucault (1966, 1969). We started by building a corpus using an incremental research strategy (the "snowball" method), starting from first bibliographic reference on history of welfare economics Baujard (2013, 2014). Then, we study the various statements within a corpus, in order to identify regularities and turning points both in semantics and concepts, so as to compare discourse "styles". Unlike other approaches in social sciences, the method of knowledge archaeology consists in analysing scientific discourses in themselves, outside the social, economic and political context that led them to emerge. Results: Using this methodology, we first examine to what extent the early utilitarianism is typical of the classical episteme as described by Foucault, which entails (i) the use of a mechanistic framework, (ii) the use of mathematics and more generally (iii) an effort to classify different entities. Second we examined how the rejection of interpersonal comparisons in the marginalist literature and the transition to ordinal utilities could be typical of the modern episteme, through the development of positivist stand and transcendental function of the notion of utility.