The subject of Annabel Brett's remarkably subtle and intricate new book is what the sixteenth-century English Aristotelian John Case called the “sphere of the city.” By this he meant, as does she, not the physical space (the urbs) but, the civitas, “a civic not a stone structure” (although, as she admits, it was not always easy to disaggregate the two). We routinely refer to this as the “state.” But in the sixteenth and seventeenth centuries, with which Brett is wholly concerned, the conception of the civitas embraced far more than the domain of sovereign authority that state theorists would later make of it. Her project is to describe how a richly heterogeneous group of authors—Hobbes, Grotius Vitoria, Soto, Suárez, Molina, Juan de Salas, and Rodrigo de Arriaga, to name but the best known—attempted to construct the idea of what she calls, “the commonwealth as a shared juridical space that transcends the natural being of its subjects.” Her concern throughout, however, is not simply with the state itself, but with the frontiers, between the human and the nonhuman, and between one human dwelling and another, and crucially with the persons who moved back and forth between them. Her authors confronted some of what have subsequently become the most pressing, and still largely unsolved, questions facing the modern state. What is the precise relationship of sovereignty to place? Can the state legitimately control the movement of its own citizens? Can it prevent the citizens of other states from crossings its borders, and even settling on its own territories? Does its jurisdiction extend to its citizens when they leave its borders? These first arose in the context of the earliest period of Europe's expansion overseas when no familiar legal arguments were at hand to help answer them. The only possible juridical order capable of providing any compelling answer had, therefore, to be expressed in terms of a supranational, universal, and consequently “natural,” law. Exactly what this was, however, was by no means simple or uncontentious, and from the early sixteenth century until the entire edifice of jusnaturalism was torn down in the eighteenth and nineteenth centuries, the identity of the natural law became the focal point of all subsequent discussions of what Brett calls the “metaphysics of human agency.” It was this metaphysics that served to build an image of the civitas, which was both a creation of human agents (Hobbes' “Artificial man”) and also something founded in nature.

Changes of State is a remarkable book in a number of ways. It offers what is, in effect, a wholly new understanding of the emergence of the modern concept of the state, and of the seemingly insuperable question of state sovereignty. By focusing, however, on the relationship of individual human actors to both the human and the nonhuman world—what she calls “the uneasy frontier between nature and the city”—Brett has been drawn into the wider question of how the different civitates related, both politically and legally, to one another. This is not merely to say that in this period the natural law, the law of nations, and the positive law were all believed to be, to some degree, interdependent, but that from its very beginning in the sixteenth century, the nation-state, which we have come to think of as the outcome of an internal process, was also conceived in terms that were inescapable external. Today, when the crossing of frontiers has become a commonplace, when the human relationship to the nonhuman, animate and inanimate, is no longer seen as self-evidently instrumental, a proper understanding of this history might well be, as Brett characteristically understates it, “still fruitful for our political thinking today.” The book is remarkable in another more purely historical way. Although Brett confesses to what she calls a “Hobbesian coloring,” her story quietly upturns what, ever since the early eighteenth century has been seen as a marked break between the neo-Thomist—that is, “scholastic”—conception of the natural law, and Hobbes' and Grotius' formulation of what Richard Tuck called the “modern natural law.” Brett does nothing to diminish the originality of either Hobbes or Grotius. (At the end of Chapter 5 she provides one of the most powerful accounts ever written of what she calls the “revolutionary strength” of Hobbes' conception of the state.) But by reading Hobbes and Grotius simultaneously with their neo-Thomist predecessors and contemporaries, by seeing them on such crucial matters as natural liberty, as “joining hands,” she has provided a far richer account of both, than any currently on offer.