Through the centuries, at the heart of Catholic moral theology is a fundamental question: How do we behave responsibly in the face of moral uncertainty? Attempts to resolve problems of everyday life led to the growth of a variety of moral systems, one of which emerged in the early 17th century and was known as probabilism. This method of solving difficult moral cases allowed the believer to rely upon a view that was judged defensible in terms of its arguments or the authorities behind it, even if the opposite opinion was supported by stronger arguments or more authorities. The theologian Juan