Who would undertake to write a history of all political thought, and why? Many a writer will assay a history of this or that political thinker (who was Hobbes?), or of how a thinker treated this or that major concept (what did Hobbes think about sovereignty?). But it takes rare ambition to attempt total histories. From a writer’s point of view—and perhaps a reader’s—Three Views of Sovereignty in Early Modern England is considerably less daunting than Sovereignty: A History from Ancient Greece to the United Nations.

There are sound reasons for political theorists to maintain a narrower focus. The history and institutions of a given society tend to restrict the range of questions and methods political theory can apply to it. Many scholars, moreover, see little value in “total histories” of concepts, or indeed in any study that goes too far beyond individual thinkers and specific questions. How, after all, can we speak of a concept of “sovereignty” persisting from ancient Athens to now? In 2013 we conceive of sovereignty in ways that would have puzzled our great-grandparents, let alone thinkers who lived centuries before the rise of nation-states. The risk of anachronism runs high. The history of thought is beset with concerns about the proper ascription of influence, the difficulty of tracing intellectual connections across thinkers and eras, and the worthiness of the traditional list of canonical texts.

With all these cautions in mind, we turn to Alan Ryan’s new book, On Politics: A History of Political Thought: From Herodotus to the Present. Ryan, a political theorist and author of books on John Dewey and John Stuart Mill, has enjoyed a distinguished career at Oxford and Princeton, and in the pages of the New York Review of Books, for over forty years. He is an elegant writer and an engaging guide to the great dead philosophers whose thoughts fill these two volumes (totaling over a thousand pages and handsomely paired in a boxed set). And in his own, subtle way, he is a bold participant in an ongoing debate over what political thought can or ought to be. On Politics is aimed at educated nonspecialist readers with an interest in politics, philosophy, or social theory—people who know a thing or two about Marx and Socrates, but perhaps not William of Ockham or Marsilius of Padua. Such readers will find here an authoritative guide to more than two millennia of Western political thought, as well as a confident, even stylish, entry into important debates within hermeneutics and the philosophy of history. On Politics is a history that doubles as an argument about what such histories can be, and what we are doing when we read them.

If Ryan is not overly didactic about these debates, neither is he shy about them. At the beginning of the first volume, he declares his belief that “the project of entering into the thoughts of the long dead and rethinking them for our own purposes is both possible and useful.” As he well knows, some of his colleagues view this notion as not only naïve, but pernicious. Such “rethinking,” in this skeptical view, encourages anachronism by allowing readers to project their concepts and their biases onto the unwilling dead, leading us to mistake our thoughts for theirs. (What would Locke think of Social Security? How would Grotius feel about the “war on terror?”) Yet, as Ryan skillfully demonstrates, we can in fact engage past writers for present benefit once we abandon the expectation that dead philosophers can “answer” our questions and the assumption that they set out to do so. There is a winning, provocative self-assurance about Ryan’s confidence that this process, if we go about it carefully, can indeed help us think through our own problems.

History, then, is the book’s main purpose, but not its sole purpose. Political theory, Ryan writes, is an instrumental discipline, “a mixture of philosophical analysis, moral judgment, constitutional speculation, and practical advice.” Studying the history of this discipline helps build the foundation for a critical examination of politics, which in turn is often a form—and always a precondition—of political action. Like all great teachers, Ryan is not content merely to fill his students’ heads with knowledge and send them away. He is inviting his readers into a discussion that, while more than a few steps removed from the world of policy and current events, may nonetheless prove politically productive.

But what is it producing? Certainly one doesn’t come away from On Politics—or any work of political theory, for that matter—in sudden possession of political wisdom, or a specific plan for addressing this or that political problem. What readers will gain is a deeper knowledge of what their forebears thought, and of how these ideas both reflected their eras and endured beyond them. Ryan writes not merely as a historian, but also as a theorist, making judgments on the coherence or plausibility of different arguments. Thinking through the ideas of past philosophers not only clarifies our own beliefs, but helps us recognize the fundamentally contingent and largely artificial nature of political life. Ideas do not simply emerge because they are good or true, and political arrangements are not simply the result of a society’s needs at a given moment. To the contrary: They are invariably the products of human thought and action, and as such they deserve careful scrutiny—applied with the recognition that things have been, and perhaps still could be, otherwise.

An important lesson in this regard, deftly demonstrated in Ryan’s book, is that there was a time before the existence of every political idea—or at least before that idea became widely known. He notes, for instance, the early glimmers of what is now called social-contract theory, espoused by Glaucon, one of Socrates’s interlocutors in Republic. That theory (which gains little traction in Plato’s text) would lay mostly dormant in Western political thought for another two thousand years. And in Aristotle’s case he points out—without anachronistically conscripting the philosopher as a democrat—that Book II of Politics offers something very close to the foundation of an argument for representative government. Aristotle, Ryan remarks, “had the right premises.”

As Ryan notes, fully realized conceptions of political representation would not emerge until the modern era. What he makes clear is not that there was a thought—call it “representative democracy”—that germinated in Aristotle’s era and traveled through the ages until it was perfected by James Madison. Instead, he suggests that certain political problems—such as how to enable self-government without turning the ship of state over to sailors who have never learned to navigate—tend to reemerge, in various forms, at different times and places. When that happens, the new generation confronting the old problem may or may not refer to the response of its ancestors. The American Founders, for one, were self-consciously involved in a highly ideological political project, and they had read their ancient philosophy. But the rest of us, to an extraordinary degree, are simply living in Aristotle’s world whether we realize it or not.

Ryan’s book helps us realize it. In the process, we see how similar we are to our predecessors—and how different from them. That much becomes clear in Ryan’s discussions of such lesser-known thinkers as John of Salisbury, the twelfth-century writer whose Policraticus asserted that while a ruler’s authority comes from God, it is nonetheless forfeited when exercised without justice. The latter half of that formulation advances an argument so familiar to present-day readers as to be almost unremarkable. But the first half’s invocation of divine authority is a remnant of a strange and remote past—a signal both of the argument’s audacity in its own era and its distance from ours. Ryan shows that the past’s power to captivate and bewilder us is bound up with precisely this admixture of the familiar and the alien.

Ryan supplements his discussion with lively accounts of political and ecclesiastical developments in Europe, from the church reforms of the eleventh century to the rise of the papal states to the Reformation. (It is, of course, of central importance to the history of Western politics that political life and religious life were entwined for so long, and Ryan’s account helpfully interweaves the intellectual, legal, and political dimensions of that history.) One rich and engaging chapter rescues Thomas Aquinas from the occasional dryness of scholasticism; another gives the early humanists admiring but not uncritical attention. At his best, Ryan writes with verve and warmth; when he advocates reading texts slowly and carefully, one imagines him savoring them like a fine cigar or glass of wine. His enthusiasm is infectious.

It also lends a sense of culmination to his work. One detects in Ryan’s narrative few of the misgivings other writers have voiced about the advent of modernity, self-government, and rationalism. Yet his narrative nonetheless avoids triumphalism, which is all to the good: we should be able to describe real historical progress without glibly assuming that the remaining barriers to enlightenment will crumble in the face of technology, or rationalism, or efficient management, or some other trendy panacea. And while some readers may be tempted to scoff at the creaky doctrines of ancient thinkers, Ryan displays enough broad-mindedness—and historical sensitivity—to understand the reasons for their daunting intellectual remoteness. He takes “very seriously the thought that over the past two and a half centuries several revolutions dramatically changed the world that politics tries to master.” Incredible, and incredibly rapid, changes in technology, demographics, literacy, and politics “have created a world that is in innumerable ways quite unlike the ancient, medieval, and early modern worlds.” It follows that even if one accepts the essential sameness of human nature across time and place, the context of human life has changed so drastically that it is now much harder to draw usable political morals from history—a favorite method of premodern political theorists.

Recognizing this, Ryan proceeds both as historian and as philosophical critic. His discussion of Tocqueville deftly weaves the French aristocrat’s background and later political career into a discussion of Democracy in America, demonstrating how that masterpiece has been misread, or selectively read, by Americans. Marx is helpfully separated from the subsequent history of the Soviet Union, evaluated on his own terms as an intellectual and a theorist, and castigated for the lapses in his work. A more reflective tone emerges when Ryan turns to “the world after Marx,” abandoning his chronological approach in favor of thematic chapters on such topics as empire, socialism, dictatorship, and democracy. He ends with a discussion of “the human future,” treating questions of religion and secularization, nuclear war, globalization, world government, and humanitarian and environmental crises. These lucid and concise discussions are intended not to introduce new concepts to the reader but to bring up political problems that demand critical examination—perhaps along the lines of one of the approaches covered in the preceding pages.

That is a perfectly appropriate place for the book to end up. As Ryan knows, even the most historically and philosophically conscious political actors cannot simply draw lessons from the great theorists of the past, and if we look to Augustine or Mill or Hegel for direct answers to our questions, we’ll likely come away disappointed. But that is not so much a defect of political theory as a reality of politics. Politics does not generate precisely correct answers the way mathematics does, and we may never agree on the ultimate goals of political life, much less how we ought to realize them. Still, there are better and worse ways to have that conversation, and to be historically illiterate and philosophically unreflective is demonstrably, unquestionably worse.

With On Politics, Alan Ryan has proved that point while providing readers with a tool for addressing it. His engrossing historical survey achieves a happy marriage of accessibility and intelligence that we are unlikely to come across again any time soon. Explaining the role of political theorists (a task, he rightly notes, that political theorists themselves are notoriously bad at), Ryan describes them as “engaged in productive, if sometimes frustrating, conversations across the centuries with their long-dead predecessors, as well as their contemporaries. They want anyone who might be interested to overhear these conversations and join in.” Readers of his genial and majestic book are well-advised, and well equipped, to do so.