This chapter places Kant’s conception of a priori laws within the framework of the legal metaphors. It introduces the relevant aspects of natural right theory and the notion of laws in the natural sciences as historical background to the legal metaphors. The main argument is that Kant’s notion of laws is embedded in his legal metaphors and his account of natural regularities as lawful also originates in the natural right framework. This serves as background to Kant’s account of the understanding as prescribing laws to nature and to thought. The background of Kant’s notion of laws in natural right and natural science shows how reason’s a priori laws are both descriptive of regularities in nature and prescriptive of valid judgements.