Book excerpt: "Public reason" is one of the central concepts in modern liberal political theory. As articulated by John Rawls, it presents a way to overcome the difficulties created by intractable differences among citizens' religious and moral beliefs by strictly confining the place of such convictions in the public sphere. Identifying this conception as a key point of conflict, this book presents a debate among contemporary natural law and liberal political theorists on the definition and validity of the idea of public reason. Its distinguished contributors examine the consequences of interpreting public reason more broadly as "right reason," according to natural law theory, versus understanding it in the narrower sense in which Rawls intended. They test public reason by examining its implications for current issues, confronting the questions of abortion and slavery and matters relating to citizenship. This energetic exchange advances our understanding of both Rawls's contribution to political philosophy and the lasting relevance of natural law. It provides new insights into crucial issues facing society today as it points to new ways of thinking about political theory and practice.