Love’s Enlightenment provides a penetrating, deeply scholarly examination of four key eighteenth-century thinkers: Hume, Rousseau, Smith, and Kant. It is not primarily about ‘love’ in either the traditional or contemporary senses of the term. Instead, the book focuses on Hume’s concept of humanity, Rousseau’s concept of pity, Smith’s concept of sympathy, and Kant’s concept of the rational love of others or of humankind (Menschenliebe). Hanley explicitly distinguishes these forms of ‘other-directedness’ from Platonic eros, Aristotelian philia, and Christian agape, as well as from the kind of romantic love that was exalted during Romantic period, and which dominates the contemporary usage of the term. Yet the book’s title is not inapt, for Hanley presents Humean humanity, Rousseauian pity, Smithian sympathy, and Kantian love of others as self-conscious alternatives to, or replacements for, the traditional understandings of love. That is, according to Hanley, the book’s four protagonists all saw the traditional forms of love as inadequate or dangerous or both, and so they each championed another form of ‘other-directedness’ that could provide many of the benefits that the traditional forms of love were thought to provide, while at the same time avoiding many of their shortcomings.

To simplify greatly, Hume, Rousseau, Smith, and Kant believed that eros (the longing to possess another individual and ultimately the beautiful itself) and philia (true friendship or brotherly love) are too particular insofar as they are limited to one or a few individuals, while agape (the love of neighbour that is so prominent in the New Testament) is too demanding insofar as it requires more love and selflessness than most people are capable of. In addition, these traditional forms of love all relied in some way on a notion of transcendence – the ability to go beyond not just the self but this world – but by the eighteenth century, the very notion of transcendence was regarded as suspect by many. For these and other reasons, Hanley argues, Hume, Rousseau, Smith, and Kant all found the traditional forms of love wanting. Yet they also recognized the need for some means of mitigating self-love and encouraging a concern for the well-being of others, especially given the egocentrism and individualism that are so often seen as endemic to the modern, liberal, capitalist world. The first three found a potential answer in a particular other-directed sentiment, while Kant found one in a particular application of reason.

Hume’s potential answer, according to Hanley, was ‘humanity’, by which he meant a kind of cool preference for the well-being of others – a modest desire to see them benefited rather than harmed. Hanley argues – persuasively, and against much recent scholarship – that the ‘humanity’ of Hume’s Enquiry Concerning the Principles of Morals represents a significant departure from, and improvement on, the ‘sympathy’ of his Treatise of Human Nature. According to Hanley’s Hume, humanity is both felt by everyone and capable of being extended to everyone, and as such it is ‘at once the proper foundation and the proper end of morality’ (p. 31). Yet humanity, as Hume conceives it, is a ‘cool’ sentiment, meaning that it is incapable of inspiring deep attachments or motivating self-sacrificing action. This coolness, however, is not just a limitation but also a strength: ‘humanity succeeds at the task of mitigating self-love within society precisely on the grounds that in asking so little from each individual it leads large collections of individuals to generate certain prosocial norms’ (p. 54).

Rousseau, Hanley argues, turned to the related sentiment of pity in hopes of effecting similar ends. The most familiar form of this sentiment in Rousseau’s corpus is the natural pity of the Discourse on Inequality, the instinctive repugnance to seeing others suffer that is felt not just by the primitive inhabitants of the state of nature but even by animals. Hanley shows, however, that in the Essay on the Origin of Languages and Émile Rousseau described and promoted a more ‘developed’ form of pity, one that relies on higher cognitive capacities and can achieve higher moral ends. Yet even this more developed form of pity, like Hume’s humanity, is incapable of generating warm, intimate bonds among people. Instead, it too serves to restrain the more aggressive forms of self-love and thereby to minimize the harm that people do to one another. Although Rousseau was hardly a liberal himself, the form of pity that he promoted in the modern world is, Hanley writes, ‘not subversive of but precisely in keeping with the minimal morality of liberalism’ (p. 94).

Sympathy, or the ‘fellow-feeling’ that results from our inclination to imaginatively project ourselves into the situations of others, plays a similar role in Smith’s thought. Hanley’s account of the main benefits and limits of sympathy will be familiar by this point: it is felt by all and is capable of being felt for all, but it cannot provide the basis for the kind of deep social connections that the traditional forms of love fostered. Instead, its ‘chief social purpose is to mitigate the main threat to the minimal bonds [that hold a liberal society together] – a threat that Smith himself squarely identifies as self-love’ (p. 123). Hanley suggests that Smithian sympathy does a bit more than Humean humanity and Rousseauian pity to give people a positive incentive to promote the well-being of others – as opposed to merely avoiding doing harm to them – insofar as Smith emphasizes that we naturally desire the esteem and approval of others, but this incentive remains relatively modest even in Smith’s thought.

Kant’s proposed means of mitigating self-love, as might be expected, was somewhat different. Indeed, he criticized the kinds of sentimentalized other-directedness that Hume, Rousseau, and Smith had promoted on the grounds that they cannot truly be extended universally, centre on mere ‘good-feeling’ as opposed to ‘good-doing’, and tend to treat others as mere objects of compassion rather than ends in themselves. The alternative that Kant offered, according to Hanley, was a love of others or of humankind that is grounded in an extension of ‘proper’ self-love (Eigenliebe) to others through reason: ‘the good and natural self-love of benevolent concern for one’s own ends is defensible before the categorical imperative only if it is extended to a similarly benevolent concern for the ends and happiness of others’ (p. 152). Despite Kant’s criticisms of humanity, pity, and sympathy, the alternative that he put forward too is both ‘wide’ and ‘weak’ – universally applicable but fairly minimal in its demands (p. 159). We must treat others with respect out of respect for the moral law itself, according to Kant, but we need not – and indeed should not – feel the kind of deep, intimate bonds with others that the traditional forms of love represented.

Hanley’s studies of these four thinkers are ‘not … for the faint of heart’, as he admits at the outset (p. 19). The discussions are frequently rather intricate, detailed, and deeply immersed in the scholarly literatures on each thinker. Yet they are also marvellously clear, and the payoff is an extremely nuanced and sophisticated analysis, one that sheds new light on the broad theme of the book as well as on each of the thinkers taken up (even if specialists on these thinkers will inevitably have quibbles here and there). Hanley is restrained – perhaps overly so – in offering his own assessment of the arguments that the book analyses so carefully; indeed, the epilogue is only three pages long. He says little, for instance, about which form of sentimentalized other-directedness – Humean humanity, Rousseauian pity, or Smithian sympathy – has the strongest claim, or whether Kant’s forceful critique of the very idea of relying on sentiment is ultimately compelling. (He does say that ‘Kant provides the Enlightenment’s most sophisticated response to the problem of how self-love can best be mitigated’ [p. 172], but that is not quite the same as saying that his critique of the sentimentalists is persuasive.)

On the even broader question of whether the whole Enlightenment enterprise of replacing the traditional forms of love with a ‘wide’ but ‘weak’ form of other-directedness was successful, Hanley’s answer is both brief and mixed. He argues that the forms of other-directedness championed by Hume, Rousseau, Smith, and Kant are indeed capable of solving the chief problem that these thinkers set out to solve, namely that of ‘mitigating the most destructive practical effects of egocentrism and individualism and selfishness in both the public and the private spheres’ (p. 19). Yet Hanley also worries that ‘the practical success of these other-directed theories … has been bought at the expense of a recovery of the love that most of us would find more fulfilling. Put differently, the eighteenth-century vision of other-directedness is in some sense necessary but not sufficient: necessary to mitigate our worst propensities but insufficient to enable us to realize our best aspirations’ (p. 172, cf. 19-23). As for whether any necessary and sufficient options are open to us, Hanley concludes by nodding toward the possibility that a return to eros or agape or perhaps some kind of ‘Eastern spirituality’ might do the trick (p. 173). But the principal value of the book rests less on these conjectures than on Hanley’s careful, sophisticated study of four key eighteenth-century thinkers and of the transformation of the idea of love that they helped to bring about.