The overall idea of this book is quite simple: that there is a historical understanding of liberty that has at its heart the quality of individual agency, which Duncan Kelly labels “propriety” and which contemporary analytical debates about liberalism have tended to neglect. This neglect is regrettable because it both depreciates the historical richness of Western political thought and undervalues a view of liberty that is deeper and more sophisticated than recent conceptions. Kelly undertakes to redress this omission with chapters that examine in acute detail the views on liberty of five key thinkers in the history of modern liberal thought from the seventeenth to the late nineteenth century for whom propriety was central. In doing so, he wishes to move the usual discussion of liberty (negative, positive, republican) onto terrain that is conceptually richer, historically broader, and much more interesting.

The details of the argument are anything but simple. The book consists of an admirably clear and lucid introduction explaining the concept of “the propriety of liberty,” followed by five contextually rich, textually sophisticated, and deeply scholarly chapters on John Locke, Montesquieu, Adam Smith, John Stuart Mill, and T. H. Green. The book concludes with a slightly disappointing chapter that focuses on the question of self-ownership, which was made famous by Locke and has been a favorite topic of much recent debate in political theory.

By “propriety,” Kelly means a conception of the appropriate connections “between governed conduct and free agency” based on the nature of personhood, the passions, and judgment. The thinkers dealt with all share a belief that the passions are the predominant source of moral motivation in humans. The liberty they valued was not the simple freedom to do as one pleases. Rather, it was the result of the complex interplay of private desires, individual judgment, and public norms and institutions. The book is an exploration of this distinctive view of liberty as a “form of appropriate or governed conduct” involving both internal and external governance. Each of the accounts of the views of the five thinkers who make up the substance of Kelly's study are insightful, delicately nuanced, and supported by reference to a very impressive, and almost unimaginably broad, range of primary and secondary literature. While it is not possible to do justice to these accounts in a short review, some features are worth noting.

According to Kelly, Locke stands at the beginning of the particular conception of liberty as a form of appropriate conduct (propriety) that is the heart of his study. His reconstruction of Locke's view of liberty is unusual for its focus on his Essay on Human Understanding rather than on his Second Treatise of Government. This is because of Kelly's interest in the inner life and governance of individuals in Locke's conception of liberty. Another distinctive feature of his account is the emphasis that he gives to the influence of Cicero's De Officiis—evidently Locke's most prized book—and the religious writings of the French Jansenist Pierre Nicole on Locke, who was a Puritan and (as Kelly points out) translator of three of Nicole's Essais de Morale in 1676. Both of these sources played a prominent role in shaping Locke's understanding of the inner self and its relationship to political liberty.

Kelly discerns a similar view of liberty “as appropriate and self-directed regulation of the passions” (p. 59) in the work of Montesquieu in the first half of the eighteenth century. Like Locke, he argued that human beings are only “properly free” if their passions are adequately regulated and constrained both internally and externally, which led him to a theory of the relationship between the inner life of the passions and the outer world of laws, norms, customs, institutions, practices, and climate that was almost unmanageably complex.

In the second half of the eighteenth century Adam Smith continued this theme in his study of early modern commercial society. Kelly's chapter on Smith is the center of his book in more ways than one, since he expressed most clearly and systematically the idea of proprietary liberty that emerges through the complex interaction of many factors. Like the other chapters, this one is subtle, impressively well informed, and obviously sympathetic.

Kelly's discussion of the propriety of liberty in the nineteenth century deals with two Victorian liberals and reformers: John Stuart Mill and the Victorian reformer T. H. Green. Rather than focus on Mill's famous essay On Liberty and Green's well-known Lectures on the Principles of Political Obligation, Kelly concentrates his analysis on the former's Logic and the latter's historical writings, particularly his “Four Lectures on the English Revolution” (1867), where the themes of free agency, character, and shared norms of justice and decorum explored throughout Kelly's book are found.

The book's subtitle refers somewhat misleadingly to an idea of liberty in “modern political thought,” although Kelly does admit in the introduction that it is “predominantly in British political thought” that this idea emerged and has been most fully developed. All of the thinkers dealt with are British except for Montesquieu, although Kelly goes to considerable lengths to stress the influence of French and German sources on his five thinkers. It is rather surprising that none of them is German. Perhaps there is something distinctively British—or Anglo-French—about the proprietary idea of liberty. Kelly does not say, and so one can only speculate on whether this was intentional. Personally, I think that some reflections on this theme would have made a very interesting topic for the book's conclusion.

The Propriety of Liberty has all of the intellectual virtues that one would hope and expect to find in the best intellectual history. It is not a light or easy read, nor (I suspect) is it intended to be. It is an unapologetically scholarly book written for scholars in a manner that is stylistically clear, conceptually rich, carefully argued, and impressively learned.