Using functionalist and genealogical frames of analysis, this article separates the function that dignity has served in law's self-legitimation from the functions that dignity plays in legal discourse. These modes of understanding dignity's function are related, but are apt to fuel scepticism about dignity if they are conflated. Dignity is an ideal challenging the idea of law as the will of the sovereign; and it is an ideal enriching law's construction of personhood. For different, systemic, reasons, dignity is a norm with unique discursive properties: it is principle, heuristic, and a peremptory norm. These differences are thrown into relief when 'function' is conceptualised in competing genealogical and functionalist terms. To the extent that these frames of reference are reconcilable, they point to dignity's core function as the disruption of law's dominant conception of sovereignty. We can conclude that dignity is a concept with problematic characteristics that can, nevertheless, be defended against charges of vacuity or redundancy.