Shagan's paradigm-busting book is much like the category of “belief” he aims to historicize: it is hard; it is almost nefariously changeable; and it is essential for understanding our present societal dilemmas. Shagan seeks to understand how belief has spilled outside of the church to be situated and revered “everywhere” today (29). Whether our contemporaries speak of “God, global warming [or] ghosts,” he notes that “The willingness not to interrogate the belief-talk of others underwrites the formation and functioning of a modern society” (7). Most interpret this latest iteration of belief as two extreme and opposing poles, either signifying a Western, “aggressive new regime of believing” or a “pandemonium of relativism” (290, 291). Shagan reconciles these by proposing an optimistic middle ground in which modern belief emerges as a “triumph of subjective opinion,” our own twenty-first-century “public sphere” (291) in which we have come to agree that “belief is a space of sovereign judgment” (288).

To argue this, Shagan must overturn stubborn schools of Enlightenment interpretation that have declared (Christian) belief dead at the hands of Reason. He contends instead that belief moved out of the Church and into the world in desperate reaction against both the sectarian exclusivity of the Reformation and the stark authoritarianism of the Counter-Reformation. Shagan ambitiously tackles Protestant, Catholic, radical fringe (Anabaptist), and Enlightenment and post-Enlightenment authors—each usually studied separately—in order to demonstrate a striking emergent complicity surrounding belief. The “common project” that drove us to modern belief was piloted by Church factions working “to make belief hard” (66), leading to people shifting belief into more manageable, secular, individual corners.

The number of corners Shagan trawls to track belief is awe-inspiring: he covers medieval theology, biblical exegesis, Lutheran and Catholic creeds, atheist tracts, spiritual diaries, missionary letters, heretical writings, dictionary entries, scientific reports, economic and mathematical theories, and Romantic poets to name just a few. He quotes liberally from many of the usual suspects: Augustine and Aquinas (chapter 1); Luther and Loyola (chapter 2); Plato, Calvin, Bacon (chapter 3); Teresa of Avila (chapter 4); Montaigne, Socinus, Grotius (chapter 5); Descartes, Jansen, Spinoza, Locke (chapter 6); Rousseau and Mandeville (chapter 7). Shagan is apologetic about sticking to this canon (26), but he need not be, because he pilfers magnificently irreverently through their writings in his search for “belief” and uncovers it there in ways that often unseat the writers’ intentions and our presumptions. For instance, he says of Montaigne that “it is hard to imagine a worse poster child for a new constellation of belief” (174); he also adamantly refuses to give Kant the last word of this story, refreshingly awarding that prized place instead to William Blake (278–279). Shagan also intentionally highlights fringe thinkers throughout, calling attention to the Jesuits in Canada (versus their more famous brethren in China), the Jansenists of Port Royal, and those like “amateur historian and professional soap-boiler Sebastian Franck” (88), all whom he quotes as equal (or greater?) articulators of the exceptionally challenging work of believing. Shagan's work is a reminder of why we keep returning to this canon, not simply because of European hegemony, but because some of these individuals thought so insanely hard and contradictorily about what it means to be human.

Indeed, the first five chapters of the book speak directly and exhaustively to the difficult labor of defining belief, such that this section devoted to origins could reasonably be subtitled “Pain.” The chapters are organized chronologically, from the medieval period through the seventeenth century, but each of them builds to anguish so much that the reader ends up identifying perhaps too strongly with the Atheist in George Gifford's 1581 dialogue who cries, “Let me alone; I believe as well as you” (90). Fortunately Shagan is not the Zealot of Gifford's dialogue. He intervenes as a compassionate guide to help the reader through these tough passages: he translates one ardent believer after another, extracting the sympathetic essence of their varied messages.

Shagan moves us from the medieval period when belief was widely perceived as participation in a collective (chapter 1) into a key watershed of difficulty in the Reformation, when Luther proposed “the first academic test for Church membership,” eliminating those who did not know the catechism (73, chapter 2). He charts the weaponizing of belief in Protestant and Catholic usage of “atheist” and “unbeliever” as versatile insults (chapter 3). He surveys intimate Protestant and Catholic personal reports of the crushing internal process of believing (chapter 4). He then ventures to peripheries and frontiers to consider encounters that necessitated changes to how believers of all stripes approached belief (chapter 5). Shagan shows a remarkable ability to discuss both Catholic and Protestant trajectories in the same chapter, acknowledging their separate complexities and inventiveness, but resisting assigning either party too much applause for transforming belief. As he puts it tartly, “any regime can be said to create the reaction against it” (127).

One would think that in his remaining two chapters—devoted to Enlightenment and the eighteenth century—Shagan would feature rationalists coming to the rescue and providing relief. But this book's finale might be more aptly subtitled, “Surprise!” In his overview of Enlightenment contributions to belief (chapter 6), Shagan instead shows scientists and philosophers like Boyle and Hume turning back to “theology … to defend the legitimacy of experimental hypotheses,” stressing that natural knowledge is “always provisional and incomplete” (227, 233). Their reappropriations accentuated belief as more probable than certain. Shagan then turns to an entertaining assemblage of the humanities (chapter 7) to deliver what is arguably the most shocking development of modern belief: “people do not have to accept that something is natural, divine or eternal to believe in it: people also believe in what they have made” (253). Here he musters Coleridge on “the willing suspension of disbelief” (250); the industries of cosmetics and artificial beauty (256); imaginary numbers in mathematics and commerce (263); and political theorists who advocated that belief in (human-created) society is what actually makes it function (266–270).

It is these final chapters that keep the work from fitting the tired mold of intellectual histories that emphasize progress with the Enlightenment as crucible. Shagan dates the birthing rumbles to earlier than the Enlightenment and does not overdo the rupture; rather, he highlights continuities of theology and creativity. He may have intended to describe modern belief as the ultimate refinement of his subject—he does conclude with an idyllic snapshot of the Metaphysical Society of London in the 1870s, with “Catholic, Protestant and atheist … engaged in debate over the nature of belief” (288) in a model manner that “enables peace in a diverse society” (291). But the rest of Shagan's work, the “hard” chapters, make it difficult to freeze the frame there and not be left, instead, with an overwhelming sense of the affinities between our current times and earlier credulities.

Particularly in the United States today, “facts” and “truth” are being weaponized and people crushed by the strenuous, now largely individual labor of sorting opinion from reality; these parallels with the Reformation period suggest that modern belief is once again being put through the wringer to become something new. As such, Shagan's work is potentially most useful not as an end-point, but as an exceptionally well-researched grab-bag of some of humanity's prominent thinkers wrestling with belief. Within this assemblage, some voices resonate today regardless of their chapter or era placement. For instance, Pascal's seventeenth-century wager (220) works as well to justify climate change as it does to explain the existence of God (a relevance noted by Shagan, 236). More than a treatise on belief, this timely book proves the past is crucial ground for helping us understand our current situation.