Ryan Patrick Hanley opens his new book by announcing, “Love is in the air” (p. 1). While this phrase initially evokes recent interest in love’s potential role in political philosophy, this itself is a prelude to Hanley’s focus on the transformation of love in the eighteenth century, through four substantive chapters on David Hume, Jean-Jacques Rousseau, Adam Smith, and Immanuel Kant. Hanley carefully—and quite rightly—characterizes these thinkers as important interventions in an age of growing epistemic skepticism. As the natural sciences progressed and gained greater legitimacy in the public mind, it was clear that once-common appeals to the “transcendent” and the “divine” were no longer adequate to bind citizens. Whereas Plato could appeal to “transcendent ideas” and expressly Christian philosophers could evoke the “divine,” growing philosophical skepticism was soon to render such appeals ineffective. At the same time, one might add, in the wake of Martin Luther’s fracturing of Christianity, the need for affective bonds was growing. The social bond of the church, such as it was, gave way to religious fragmentation and warfare throughout Western Europe. Beyond this, as Hanley aptly suggests, recent transformations in the direction of a market or commercial economy had begun to privilege egoism or self-love (e.g., p. 16) at the expense of traditional notions of caritas or agape. Indeed, if “love was in the air” in the eighteenth century, it was because its services were desperately needed.

The first intervention to stem encroaching modern egoism, on Hanley’s narrative, was David Hume’s “politics of humanity,” which, as he notes, was less technically a philosophy of love than an achievable alternative to love for a world where a “universal and disinterested love of others is a chimera” (p. 34). While Hume had flirted with sympathy as fulfilling this role in his Treatise, Hanley finds a more substantial theory of “humanity”—or a “cool preference of what is useful and serviceable to mankind” (p. 51)—in subsequent writings. The great virtue of the sentiment of humanity, unlike with sympathy for Hume, is its capacity to inspire goodwill toward those far removed. It is, for Hume, the one natural sentiment that is “so universal and comprehensive as to extend to all mankind” (p. 45). It also possesses the advantage of being universally felt by moral agents. However, the problem with Hume’s approach is in its very “coolness”—insofar as it is weakly felt, it can fail to inspire actions.

The second substantive chapter addresses Rousseau’s “politics of compassion,” in which Hume’s onetime friend crafts a response to the growing specter of egoism and amour-propre with an appeal to and development of pitié. Hanley’s Rousseau does not rely lazily upon natural and unrefined compassion, but rather carefully refines this natural resource—particularly in his Essay on the Origin of Languages and Emile—with the faculties of idea formation, judgment, comparison, and reflection (pp. 79–83). This culminates in Emile’s Book 4, in which Rousseau declares that “the love of mankind is nothing other than the love of justice,” where pity is “extended to the whole of mankind” (p. 91). While there is much that is inspiring in Rousseau’s efforts here, however, Hanley emphasizes the limits of Rousseau’s approach as well, including Rousseau’s own worries about its efficaciousness and its tendency to set the objects of pity below those engaged in pitying.

A third attempt to reform love for modernity can be found in Hume’s friend and Rousseau’s admirer, Adam Smith. As with Hume and Rousseau, Smith is particularly concerned about the dangers of egoism in the emerging market economy, even as he well understands that economy’s social benefits. Smith’s response can be found throughout the Theory of Moral Sentiments in his understanding of sympathy. The great virtues of sympathy, on Hanley’s account, include its “universal extension and universal accessibility” (p. 120), much like Hume’s conception of “humanity.” Yet Smith concedes a particular problem with sympathy, namely, its “dull sensibility to the afflictions of others” (p. 122), which is particularly disconcerting when applied to the inability of people to feel genuine sympathy for the poorest among them. To a degree, Hanley argues, Smith seeks to mitigate sympathy’s limitations by emphasizing that one’s social status is at least partly contingent upon being perceived as a good and sympathetic person in others’ eyes. Yet he concedes, as such, that Smith’s theory of sympathy depends on incentives that have little to do with sympathy or love.

Perhaps the most surprising and radical chapter of the book is its treatment of Kant, which, Hanley wryly concedes, might appear to be “looking for love in all the wrong places” (p. 135), given Kant’s reputation as the least romantically inclined of the eighteenth-century philosophers. Yet in tracing Kant’s largely ignored thoughts on love from his precritical writings to his Tugendlehre, Hanley persuasively reveals the Königsbergian’s persistent engagement with love. As he argues, while Kant was consistently dismissive of acting from mere love or sentiment, he actively promoted willing to love (p. 150)—a Kantian method of squaring a circle that includes both sentiment and reason. As such, he develops a “duty to love others that emerges strictly from pure reason” (p. 151). While Hanley celebrates Kant’s achievement in the philosophy of love as “striking” and indeed the “most sophisticated response to the problem of how self-love can be best mitigated” (p. 172), he concedes that Kant’s approach may well fail to capture how most people experience love, certainly when compared to Hume, Rousseau, and Smith.

There is a great deal to recommend in Love’s Enlightenment. It represents an impressive achievement in its textual analysis of four of the most important thinkers of the eighteenth century. I have some minor quibbles on small matters of interpretation concerning individual thinkers. For example, I am less sure than Hanley that Rousseau is operating in the Emile on the assumption of “an unavailable transcendence,” when the intellectually modest pupil himself is described as understanding ‘‘[t]he true principles of the just, the true models of the beautiful, [and] all the moral relations of beings” (Emile, or On Education, trans. Allan Bloom, [1762] 1979, p. 253). But this is a minor difference of interpretation where there is admittedly great diversity of scholarly opinion. On the whole, however, Hanley demonstrates himself to be a master interpreter of Enlightenment political thought, and his timing could not be better for a generation that arguably needs to recapture love’s utility more than ever.

In terms of future research directions, it is worth noting that Hanley does not investigate what happens in the post-Enlightenment history of love. But this book study surely merits a sequel. While one cannot trace that history adequately here, this story would seem to culminate in the career of someone like Jürgen Habermas, who has dedicated the bulk of his career to a growing reliance on reason, with relative indifference to forging affective social bonds. In this way, one might argue that Habermas is the logical outcome of Hanley’s characterization of the Enlightenment’s mission to forge societies without the benefit of “transcendent” or “divine” bonds. Throughout his extended discourse-ethics period, Habermas sought to construct a society based almost entirely on pure reason. But as he himself has begun to acknowledge, such approaches have real, almost crippling, limits. A society ignoring those affective foundations—that Hanley locates in ancient conceptions of love characterizing the Greeks and early Christians (pp. 7–17)—may find reason to be inadequate for the purposes of forging cohesive, thriving societies. Without those underlying bonds of feeling, Habermas now worries, citizens become “isolated monads acting on the basis of their self-interest alone, persons who use their subjective rights only as weapons against each other” (Jürgen Habermas and Joseph Ratzinger, Dialectics of Secularization: On Reason and Religion, 2007, p. 35). One only needs to read the “comments” section of the local newspaper, not to mention any number of online fora, to worry that Habermas is all too accurate here.

The question that remains for Hanley, then, should he pursue this worthy history further, is whether such a state of affairs represents a failure of reason or a failure of love as the Enlightenment conceived it—as embodied in the four subjects of this book—or both.