“What is love?” This question perhaps was most famously posed by the mononymous 1990s philosopher-poet, Haddaway. Among the ponderers of this question, Enlightenment philosophers such as Hume, Rousseau, Smith, and Kant are not as easily remembered, lacking as they did Haddaway’s infectious hook. That Adam Smith might be considered a philosopher of love is surprising given that he was a lifelong bachelor who seems not to have had a romantic bone in his body. And Kant derided romantic love as pathological. But love was in the air even in the Enlightenment, as Ryan Patrick Hanley argues in his recent book Love’s Enlightenment.

The philosophers covered in Hanley’s book considered the nature and grounds of love and in many ways inaugurated the roots of the modern shift away from traditional forms of transcendental love toward “sentimentalized other-directedness.” Hanley identifies the Enlightenment as the stage in which “the appeal to transcendence was dethroned from its traditional primacy.”

The major Enlightenment figures who theorized about love were not seeking to debunk religion. They were seeking something more modest—namely, to place ethics (and specifically, love) on a universally accessible, non-transcendent footing. Hume grounded love in a sense of “humanity,” or a preference for others’ well-being; Rousseau developed the concepts passion and pity; Smith saw sympathy as surpassing the notion of universal charity; and Kant “grounded the love of others in a rational extension of self-love.” Hanley persuasively argues that these thinkers made brilliant and innovative efforts to check egocentrism and to promote the other-directedness that modern liberal society requires.

But were their efforts successful? In the end Hanley wonders whether the creative and erudite accounts of love that were developed by Hume, Rousseau, Smith, and Kant are really sufficient for a full and satisfying account of love, or whether their cutting off of the es at too great a cost. In the words of another 1990s muse, sometimes enlightened love “just ain’t enough.”