I examine the deployment of health equity in public health discourse and practice, theorizing its journey from its original commitment to social justice vis-à-vis injustice. As an empty signifier and vehicular idea, health equity is invoked within an infinitely extendable field of discourse and practice. Secondly, I analyse how health equity is made knowable through modes of measurement and representation. I argue possibilities for understanding and acting upon health (in)equity are shaped and limited by evidentiary norms/imperatives embedded in the rules of institutional fields. I historicise these evidentiary norms as mechanisms of government dating back to the enlightenment. By legitimizing and deploying action according to evidentiary productivity rather than normative-political reasoning, government effaces itself. I examine the relationship between precise but incomplete knowledges and justice, showing that however precise our knowledge is, if we do not engage with its incompleteness, we will always miss the mark, and inequities will persist.