This chapter describes a widespread tendency in the social sciences to lose sight of the singular existence and personal experience of every human being in favour of the primacy and stability of social phenomena. Interchangeability constitutes a crucial element for understanding why and how the social sciences encounter difficulties grasping human singularity and subjectivity. A typology of various kinds of interchangeability is offered, combining two different forms: the interchangeability of individuals and the interchangeability of perspectives. Finally, the anthropological and phenomenological conditions that must be fulfilled to construct a social theory without interchangeability are discussed.