The article analyses the relation between sovereignty and life in Michel Foucault’s criminological and psychiatric studies. His critique of the juridical subject is centred on modifications of penalty. But the real basis of the deconstruction of juridical subjectivity is the bio-medical epistemology. In xix century, the power of decision as decision of death is not actual yet. Sovereignty is really a power of death. The life becomes a limit. What kind of limit? Abnormals and hermaphrodites are figures of this limit. They show how life, biological life, designs modern political strategies. Epistemology becomes a key of Foucault’s critique of political reason.