This chapter examines the interpretive consequences of Amartya Sen’s ontological reticence. While Sen recognises the social world as open and processual, his continued reliance on formal, taxonomic methods generates a deep tension that shapes how his work has been received and operationalised. It is argued that the plurality of interpretations surrounding the capability approach reflects not theoretical flexibility but ontological ambiguity. Drawing on developments in Social Choice Theory and mainstream empirical modelling, the chapter shows how Sen’s framework has been adapted within methodologies that presuppose closed systems, thereby diluting its relational orientation. It then contrasts these uses with heterodox applications that foreground an evolutionary outlook. Finally, by examining the contributions of Nussbaum and Robeyns, it is highlighted how liberal conceptions of personhood reinforce ontological inconsistencies and preliminary counters to their claims are offered. The chapter concludes by reflecting on the stakes of these tensions for the future development of the capability approach and its role in the revival of political economy.