Kantian Ethics and Environmental Philosophy is one of the first of its kind. This monograph connects the dots between Kant’s philosophy and the climate crisis, drawing from Kant’s account of the highest good, hope, and virtue placed against the backdrop of his reflections on the environmental disaster in Lisbon of 1755. Although primarily a contribution in Kant studies rather than environmental philosophy, the book fits alongside more recent book-sized contributions connecting Kant and the environment, including Brady (Reference Brady2013), Svoboda (Reference Svoboda2015), Baumeister (Reference Baumeister2022), and Vereb (Reference Vereb2025).Footnote ¹ Brady, however, focuses mainly on Kant’s sublimity and environmental philosophy, Svoboda on an environmental ethics reading of Kant’s account of virtue and teleology, Baumeister on Kant’s theories of anthropology vis-à-vis environmental justice, and Vereb on Kant’s relevance for issues such as species extinction, geoengineering, and climate corruption.

While in some ways comprehensive in their scope, it is also noteworthy that these books do not bring in ancient philosophers and the concept of hope when thinking about environmental crisis. Heneghan’s book does both and more, by exploring Kant’s account of the highest good and his view of radical hope, updated in a creative way, and marshalled to help us cope with our current environmental predicament. In an age of worsening environmental pessimism and anxiety, a book-sized work on Kantian hope is certainly welcome. Indeed, the American Psychiatric Association (2025) cites that one-third of Americans worry about climate change weekly, and a survey from The Lancet indicates that 59% of the 10,000 young respondents from ten countries were very or extremely worried about climate change (Hickman et al. Reference Hickman, Marks, Pihkala, Clayton, Lewandowski, Mayall, Wray, Mellor and van Susteren2021). Heneghan’s book, then, is timely.

A rough outline of the book is as follows. Chapter 1 sets the stage for a discussion of environmental catastrophe from a Kantian perspective. It does this by revisiting Kant’s reaction to the Lisbon earthquake of 1755, which had a profound effect on the thinking of philosophers and theologians of the time. Introducing his engagement with the ‘problem of the highest good’, Heneghan claims Kant had it in mind while penning his pre-Critical earthquake essays. The problem is that virtue and happiness seem to come apart, as evidenced especially in the case of Lisbon by the apparently virtuous churchgoers destroyed during service while sinners outside survived. In a more general respect, the basic idea behind the problem, which Heneghan understands ancient schools of philosophy – especially Stoic and Epicurean – as trying to resolve, is that there seems to be a disconnect between our pursuit of the good (virtue) and being happy (content, satisfied, having our inclinations fulfilled). Thus, Heneghan claims that ‘the problem of the highest good occupies a central and overlooked place in Kant’s ethics’ and that ‘Kant was first drawn into moral philosophy through his occasional writings on optimism and the Great Lisbon Earthquake of 1755’ (45–6).

Chapter 2 sees Heneghan relying on peripheral textual evidence (notes, lectures, the Dissertation, etc.) from the 1760s and 1770s to make the case for Kant’s critique of the ancient analytic solution to the problem of the highest good, which is a reductive one. That is, both Epicurean and Stoic schools attempt to explain the problem away, either by reducing virtue to happiness or happiness to virtue, respectively. Heneghan’s comparative analysis contributes to the literature by putting Kant’s often implicit (at least, in the second Critique) objections to competing ethical theories in clearer light by relating them to this problematic. And indeed, a lot of the secondary literature on Kant and the highest good fails to engage with Kant’s assessment of other ethical theories, especially ancient ones. According to Heneghan, Kant concludes during this period that ancient views on ethics are ultimately incompatible with what he takes to be the proper understanding of human nature, which is a dualistic one as he later fleshes out during the Critical period. Kant also concludes, Heneghan reports, that these ancient views are internally inconsistent.

The third chapter explores synthetic solutions to the problem of the highest good, namely accounts submitting that virtue will lead (causally) to happiness, which Kant thinks is refuted by experience. There is a long discussion of the Critique of Practical Reason in this chapter, as well as an interesting engagement with the correspondence regarding what Heneghan takes to be Maria von Herbert’s nihilistic criticism of Kant’s ethics. The chapter concludes by reconstructing Kant’s Critical solution to the problem of the highest good, which, having been discussed comparatively alongside ancient attempts at a solution, appears in contrast with Kant’s emphasis on hope.

The fourth and final chapter, on radical hope, takes creative liberties with Kant’s individualistic solution to the problem of the highest good, this time presenting a ‘socialized’ version,Footnote ² scaled up to help us rethink contemporary environmental issues such as anthropogenic environmental collapse. Proposed solutions to climate change – such as emission reductions and the institutional and behavioural changes required for them to obtain – present a clash between duty and material aspirations, which Heneghan takes to be a modern iteration of the problem Kant sees in the Lisbon catastrophe. Kant’s view of radical hope, Heneghan claims, presents one way to help us cope with the present challenge, being neither dogmatically optimistic nor properly pessimistic:

In the context of climate change, Kant’s view is commissioned to help us survive the Scylla and Charybdis of the crisis, namely unfair burdens and moral hopelessness on the one hand, and egoism and cynicism on the other. Heneghan concludes his chapter on hope by synthesizing Kantian views with a ‘quasi-Aristotelian’ form of courage (124) as well as the insights of Crow Tribe Chief, Plenty Coups. The book ends with a nod to Hesiod and Plato in the context of Kant’s ‘hopeful pessimism’ and a discussion of the challenges of the COVID-19 pandemic understood as a microcosmic analogue of the climate crisis.

Besides its clarity and readability, one place where Kantian Ethics and Environmental Philosophy shines (and where it differs most from recent attempts to connect Kant and the environment) is by utilizing previously underappreciated Kantian texts, especially those where Kant questions the connection between virtue and happiness. More specifically, though Heneghan relies a great deal on the second Critique and ideas from the Religion, one unique way that he brings Kant closer to environmental thought is by looking into what are usually considered non-philosophical writings in physical geography and anthropologyFootnote ³ and of course in particular Kant’s essays on the traumatic Lisbon earthquake. Heneghan sees in the pre-Critical reflections on environmental catastrophe an impetus for Kant to work out his own inchoate moral thinking, which at least in some pre-Critical works (such as the Universal Natural History) appears more naturalistic and Epicurean in its metaphysical presumptions.Footnote ⁴ Heneghan understands Kant’s development toward his mature moral philosophy as being guided, tacitly (but which Heneghan attempts to draw out more explicitly by relying on Kant’s Nachlass and lecture notes from the 60s and 70s), by his attempt to resolve the problem of the highest good.

By utilizing underappreciated Nachlass fragments, Heneghan convincingly shows that behind the scenes of the Dialectic of the Critique of Practical Reason lies Kant’s deeper commitment to ideas in the history of philosophy. The Stoics resolve the problem of the highest good by reducing happiness to virtue (blessed contentedness in being good), and the Epicureans and other naturalists solve the problem by reducing virtue to happiness (being good simply means to wisely pursue one’s inclinations). Heneghan sees Kant dissatisfied with both solutions. The Stoic is happy for us to give up on happiness by redefining it, while the Epicurean demands we disregard moral virtue altogether in pursuit of well-being.

Environmental philosophers drawn to the book’s title might be wondering how this compelling discussion of Kant might bear on environmental philosophy. Indeed, half of the book’s chapters are not concerned with environmental problems (Chapters 2 and 3), but rather theoretical problems in Kant studies (making sense of Kant’s highest good and its relation to his ethics, questions of religion vs secularism in Kantian ethics, etc.) and comparative questions in the history of philosophy (e.g., exploring to what extent Kant was influenced by ancient philosophy, despite his citing the ancients only briefly in his published works). To be sure, we have to understand what Kant says before we can apply all this to the environment, and Heneghan does attempt to show in his final chapter on Kantian radical hope (and his brief conclusion on Hesiod and Plato) that these reflections should be understood as resources for us to ‘cope’ with a socialized problem of the highest good in the Anthropocene. But perhaps the balance could be better, with more attention given to the application.

Reading the book, one gets the sense that Heneghan’s primary concerns are with problems in Kant studies and comparative ancient philosophy, and so the reader is left yearning to know more about how Kant’s thoughts on the Lisbon crisis inform our present crises. How, for example, would the socialized view of Kant’s ethical theory illuminate moral or legal duties regarding endangered species, resource depletion, carbon footprints, or pollution? Is it just a means for psychological coping or can it justify determinate action, rendering the secularized account of hope rational? Do Kantians have new environmental duties given the innovative reading of Kant and the highest good? To be fair, though its title includes ‘Kantian ethics’, the book’s account is intended to lie at the intersection of ethical theory and the history of philosophy, not applied ethics, so it cannot be faulted for failing to engage the environmental ethics literature. And the concluding remarks of the book, which touch on the COVID-19 pandemic, do offer a thoughtful analogy for a Kantian approach to global ethics, which could be fruitfully expanded upon for future investigations, climate change included.

While the discussion of the environment is unfortunately brief, the book’s strengths include its creative engagement of Kantian theory with Crow Tribe leadership insights, a reconsideration of the underexplored correspondence with Maria von Herbert, and rich contributions to ongoing debates on the highest good in Kant – even if its discussion of the environment is cut short. I would recommend it to Kant scholars working on any issue in Kant, especially his Critical thought or those with an interest in the burgeoning Kant/environment literature. I would also recommend the book to readers who are interested in existential and perennial questions rather than merely scholarly ones, especially those who wonder how Kant’s views in the Critique of Practical Reason and Religion could help us grapple with crises, just in the same way that the Lisbon crisis and French Revolution did for Kant.