The religious epistemology of John Henry Newman offers an avenue, unexplored by scholars, for interpreting moral doctrine today. Although he did not write any work on moral theology, a systematic account of the interaction between conscience and moral law in his writings can illumine foundational concerns about personal morality and episcopal authority in the Roman Catholic Church. In reaction to the rationalism of the Enlightenment Newman had remarkable confidence in the capabilities and trustworthiness of the personal, historical reasoning of individuals and ecclesial communities alike—a type of reasoning that he recognized as the driving force for the genesis and the application of moral law. Not surprisingly, his concern for historical moral consciousness, with its emphasis upon subjectivity, generated a significant shift from abstractness to concreteness in theological method, a shift that would later influence the thought of Bernard Lonergan. To illustrate the contemporary relevance of Newman's commitment to personal reasoning in theology, his explanation of the legitimate authority of conscience and doctrine provides the basis for an instructive critique of the document On the Interpretation of Dogmas (1989) from the International Theological Commission.