The concept of purely penal law, as developed by the Spanish Jesuit Francisco Suárez in the early seventeenth century, argues that promulgated law is neither morally binding upon the citizen nor conceived as a moral requirement by legislators. Rather, the law is strictly punitive in its intent and function. The theory, which grants the individual the right to determine law’s rational and moral significance, touched off a heated debate that has been renewed at various times in history yet has not resurfaced since the mid-twentieth century. This article argues for the veracity and legitimacy of the concept in light of contemporary legal and penal dynamics. It also argues that the Catholic Church should take notice of its insights in its understanding of the relationship between church and state.