All of the current prevailing theories of criminal punishment ultimately depend on some sort of normative argument to justify why the state may penalize people found guilty of crimes. Yet each of these theories lacks a strong epistemological foundation to explain how we can know what form punishments should take. This article analyzes the epistemological gaps in the predominant theories of punishment and finds that the putative epistemological sources they do use fall short of actual knowledge. The lack of an epistemological underpinning for punishment puts the very validity of punishment in doubt. Systems for quantifying punishment, such as proportionality and sentencing guidelines, only lend an appearance of knowledge to penalization. They are not true epistemological arguments. Although social norms may at first seem to provide the bases of the requisite knowledge, norms are themselves epistemically difficult to identify, let alone prove. The article concludes that a sound epistemological basis is intrinsically unattainable in the practice of criminal punishment. The best that we can achieve as an epistemologically justifiable punishment is to follow the regulative principle of “suitability” by relying on a mixture of social norms and specific empirical observation.