Cardinal Newman in the nineteenth century demonstrated that Catholic doctrine has developed over time. But Newman never considered the possibility of development in the Church's moral teachings. John Noonan takes up this task and shows clearly that in three cases—slavery, usury, and religious freedom— the moral teaching of the Catholic Church has changed definitively; what had been taught is now seen to have been erroneous. In a fourth case—divorce—change in the teaching is in process. He asks how it is possible that what is intrinsically evil in one era is not so in another.

More than half of the book is devoted to the development of the teaching on slavery, Noonan's prime case for development. For nineteen hundred years the Church resisted the teaching that slavery was sinful. Slavery at the time of Jesus and Paul was taken for granted; it was what Noonan calls an "unknown sin," an act which was not known to be sinful. Neither Jesus nor Paul called for the abolition of slavery. Among the Fathers, only Gregory of Nyssa criticized slavery. Medieval popes were slave owners. Slavery continued to exist in the Papal States into the nineteenth century. Thomas Aquinas did not find slavery unnatural. Cardinal Newman argued that slavery was not intrinsically evil. It was not until the Second Vatican Council in 1965 that the Catholic Church categorically condemned slavery. By this time the Catholic faithful had known that slavery was wrong for at least a hundred years; the Magisterium caught up with the body of the faithful at Vatican II. What is so remarkable is that neither the fathers at Vatican II nor Pope John Paul II who finally, in Veritatis Splendor, declared slavery to be "intrinsically evil," seem to recognize or acknowledge that they are changing longstanding moral teaching.

Noonan shows that there are multiple causes for the social movement toward the abolition of slavery but that the Catholic moral teaching developed almost entirely outside of the domain of the moral theologians. From 900 to 1100 a new lay social consciousness developed with no direction from Church leaders. Warriors simply stopped enslaving prisoners of war. Noonan suggests that these soldiers developed a greater appreciation of the humanity of the enemy and the inappropriateness of enslaving them (even as they continued to try to kill them). By 1300 slavery had disappeared in England and France as serfs replaced slaves. Eventually the standard titles to slave property—war, punishment, self-sale, birth—were called into question. The Christian case against slavery was developed by the eighteenth century Quakers but it took more than a century to catch on.

The moral teachings on usury and religious freedom also illustrate how development comes out of the confrontation of "difficulties" and how the faithful are often ahead of the theologians in developing the empathy that leads to a deeper understanding of Christian revelation. The theologians are often held back by their reliance on precedent.

Noonan insists that the limits of the doctrine of infallibility be respected; if the Church is infallible only under certain conditions then the rest of the time it is fallible. Certain moral doctrines are now seen as wrong because experience has demonstrated their error. But he cautions that we not judge people living in earlier times because their moral rules had not reached the level of development we know. People can only be judged according to the moral standards they know. He suggests that a church that admits that some of its past moral teachings were inadequate need not fear loss of moral authority any more than a parent who admits to mistakes in childrearing or a judicial system that allows for appeals.

Noonan argues that moral teaching is developed through the tools of analogy, balance, logic, and experience (ABLE). But the only rule of development is the rule of faith—that an increase in love leads to increase in knowledge and insight into the meaning of revelation. It was through greater empathy for the other that Christians came to realize that enslaving human beings was wrong.

The Church cannot change in that she is entrusted with the preservation of the "deposit of faith," an unchanging and final revelation. But the Church can, and has, and does change as the experience and empathy and reflection of the faithful generate new insights into that revelation.

This is a carefully researched and documented study. It is very readable and is recommended for anyone interested in the moral teachings and moral authority of the Catholic Church. The implications for the possibility of development in moral teachings presenting "difficulties" today are hopeful.