A distinctive feature of human life is our preoccupation with death. We create rituals around death, write books about our fear of death, go to support groups to cope with the death of loved ones, and even theorize about the meaning that death gives our lives. The elaborate relationship humans have with death might make one think that humans’ understanding of death is fundamentally unique, separating us from non-human animals. In her recent book, Susana Monsó aims to show us that humans are not as unique in our understanding of death as one might think. Through her careful explication of conditions necessary for concept possession, and her extensive investigation into cases where animals face death, Monsó argues that animals have a concept of death that shares core components with our own.

The book’s first three chapters provide an introduction not only to Monsó’s project on animals’ understanding of death, but also to the major trends, concepts, and methodologies in the philosophy of animal minds central to her project. These introductory chapters are a major strength of the book; their clarity and accessibility make this book great for students looking for an entry point to the field. By the end of these three chapters, students will be exposed to the history of the philosophical dispute over animals having minds, a survey of different methods available for studying animal minds, along with their benefits and drawbacks, and a critical warning against anthropomorphism (projecting too much onto animals), anthropectomy (projecting too little on animals), and anthropocentrism (focusing too much on things that matter to humans). Additionally, if the clarity and intrigue of the text is somehow not enough to keep a student engaged, the humour Monsó brings to the book will.

Monsó’s description of concepts in chapter 2 is especially noteworthy for its pedagogical value. She lays out a series of subcomponents of concept possession that build upon each other, including reliable categorization, location within a network of associated meanings, the capacity to draw inferences within this network, and relative detachment from specific sensory stimuli. Monsó provides clear examples for each subcomponent, making it easy for an unfamiliar reader to grasp complex ideas with confidence.

One should not, however, take the pedagogical virtues of this book as evidence that it will be of less interest to more advanced readers. Monsó’s position on concepts is a substantive take that challenges received views. For instance, many philosophers, following Fodor (1980), take concepts to be discrete elements in thought that make up a sentence-like, predicative, or logical structure. Monsó’s account does not require compositional structure, so philosophers who have attempted to stay closer to Fodor’s account while discussing animal concepts (for example, Beck 2012) are likely to set a higher bar for attributing a concept of death to animals. The challenge for them is to accommodate the examples of animal inferences that Monsó offers or else to adopt her less demanding view of concept possession. Certain readers, however, might wish for more clarity on the distinction between Fodorian ‘atomic’ concepts and the associative and inferential connections that might be assigned to conceptions rather than being core features of the concepts themselves. For such readers, viewing two of Monsó’s conditions as being about conceptions rather than being core to the concept may be more to their liking. The question of what belongs to the concept and what belongs to the conception raises thorny issues around the analytic–synthetic distinction that Monsó does not tackle, and neither shall we in this review.

In chapter 4 Monsó describes what she calls the ‘minimal concept of death’, consisting of a demonstrated understanding of the non-functionality of the deceased and of the irreversibility of that state. An affirmative demonstration of these features should also be calibrated to what animals can be reasonably expected to be familiar with, allowing for species and individual variation in the concepts of death. Monsó concludes chapter 4 by arguing that the minimal concept of death also fulfils the various characteristics of a concept described in chapter 2. She considers the human concepts of death to entail extra conditions, such as understanding the inevitability of death. Monsó argues that these extra conditions are not necessary for possession of a concept of death. The minimal concept also accommodates variation in concepts of death among human cultures and traditions.

Chapters 5 and 6 address understanding of non-functionality and irreversibility in a variety of animals. Chapter 5 serves as a further warning against anthropocentrism, reminding the reader that the human way of reacting to death is not the only way to react to death. This is essential to keep in mind, as Monsó writes, because we might otherwise misinterpret behaviours, totally ignore some behaviours, and focus too much on grief. Grief, Monsó argues, is just one of several possible emotional responses to death. As such, it is distinct from having a concept of death and animals who may never once feel grief could still have a minimal concept of death. Chapter 6 sets aside emotional reactions to death and looks for evidence demonstrating understanding of non-functionality and irreversibility in an immense survey of reported cases. Throughout, Monsó emphasizes the varying perspectives of animals from different species that lead them to react differently to death while still meeting the criteria for the minimal concept of death.

Toward demonstrating understanding of non-functionality, Monsó argues that animals must first be able to detect behaviour that is anomalous according to their expectations of a functioning, living being of that kind. The most compelling examples of this ability are elephants helping distressed peers, dolphins trying to help a dying peer stay afloat, and various instances of animals giving special attention or treatment to their peers who have physical disabilities. Monsó continues the argument by pointing out the importance of detecting and understanding functionality and non-functionality for survival in socially dependent species. Given this importance, it is likely that these abilities would be favoured by natural selection in social species. Furthermore, while this ability is often seen between members of the same species, Monsó stresses that it is also possible between members of different species

One can find further support for this claim beyond Monsó’s book by turning to neurobiology. Recent studies found that mice have a reliable drive to help unconscious peers, and the paraventricular nucleus and the medial amygdala were identified as brain regions crucial for facilitating this drive (Sun, Wu et al. 2025; Sun, Zhang et al. 2025). The identification of crucial brain regions for this drive might also open up new directions for research in comparative neurobiology investigating how these regions are conserved across species, which would help strengthen Monsó’s conclusion that many animals will be capable of processing non-functionality. However, the neuroscientists suggest that the drive to help, which is dependent on an ability to recognize non-functionality, is innate, likely because of its importance for survival in socially dependent species. The status of recognition of non-functionality as an innate ability suggests that it is non-conceptual, unless concepts can be innate. This raises some questions for Monsó’s view that she does not address directly, such as whether conceptual content may include non-conceptual elements.

Finding irreversibility is a trickier matter, because of its temporal element. The temporal element has led some researchers (for example, Brosnan and Vonk 2019) to stipulate that animals would need abilities for mental time travel or counterfactual simulation to grasp irreversibility. Monsó argues this is not the case and instead that processing irreversibility can be thought of as ‘the recategorization of an animal from the class of individuals from which one expects the typical functions of her species to the class of individuals from which one does not expect these functions’ (p. 134). According to this, there is no need for the subject to conceive of her own expectations in the future. Rather, it suffices that there be an enduring change in her expectations at any given moment; such an expectation is about the immediate future, but it need not have any temporal concept as part of its explicit content.

This way of thinking about irreversibility is quite compelling. There might remain, however, a question of whether reclassification adequately captures what it means to understand irreversibility. If reclassification from functional to non-functional is possible, it seems equally possible to reclassify again from non-functional to functional. Indeed, something like this must happen if an ailing dolphin is supported well enough to recover. Given that this kind of reclassification is possible, it seems unlikely that reclassification of functionality alone is sufficient for grasping the irreversibility of death. Situations where death is reversed are rare, so there are few occasions for further reclassification, but further reclassification is technically possible. Take, for example, Monsó’s suggestion (p. 135) that a lion would be surprised if a gazelle they caught and had killed suddenly got up and ran away. She takes it that such surprise would demonstrate the expectation that the non-functionality of the gazelle was not reversible (in contrast say to a sleeping gazelle). However, Monsó’s surprised lion also suggests that reclassification back to functionality is possible. If a non-functional individual can be reclassified to functional, does this demonstrate a grasp of irreversibility? The notion of classification as non-functional captures why animals might behave in certain ways, such as abandoning the corpses of their peers, but it may not completely capture irreversibility. Nevertheless, these worries should not lead one to conclude that animals are not capable of processing irreversibility. Monsó’s examples of animals processing irreversibility are suggestive enough to warrant further investigation of animals’ capacities to reason about the future and the relation of this capacity to processing irreversibility.

Monsó concludes chapter 6 by arguing that in addition to non-functionality and irreversibility, many animals will be capable of recognizing other features related to the concept of death, such as universality and causality in some sense. Thus, in addition to many animals having a minimal concept of death, widespread abilities for association and inductive generalization will mean that animals closer to humans have a more complex concept of death, which Monsó terms the ‘natural concept of death’ (p. 142). She also considers that animals may even understand their own mortality, but after considering the current evidence available surrounding issues like suicidal behaviour in animals, concludes that we do not have enough evidence to answer this question yet.

Chapter 7 is the final substantive chapter, and provides Monsó’s unique contribution to thanatology, providing her with the book’s title, Playing Possum. Monsó has argued throughout the book that philosophers and scientists have proceeded too anthropocentrically. In this chapter she argues that because of this, the field has mostly ignored the extent to which animals are much more exposed than the typical authors and readers of academic books to violence resulting in death. The chapter surveys coalitional attacks, infanticide, and predation to determine what these reveal about animals’ concept of death. Monsó explains that there are multiple degrees of deliberateness possible in causing another’s death, and only in the highest of these levels would a concept of death be necessary. In coalitional attacks, infanticide, and predation, Monsó gives compelling arguments that while certainly not all cases are a result of higher-level cognition, there are abundant instances that demonstrate an explicit intention to kill, that is, to cause death. Monsó concludes the chapter with a riveting discussion of thanatosis, the defence mechanism by which North American or Virginia opossums (commonly known in the US as possums) and other animals play dead. It demonstrates a concept of death not in the opossum or other animals playing dead, but in the predators whom thanatosis is meant to deceive. Specifically, looking at other prey defence mechanisms, Monsó concludes that if thanatosis evolved, it is because there is an advantage specifically from appearing dead (not just immobile) to animals who possess a concept of death. (And, we would add, not merely dead but so far gone as to be unpalatable.)

For anyone looking to better understand animal minds, this book is a great place to turn. Death is uncomfortable to think about, but Monsó has shown that studying death can help us understand the creatures we share the world with much better. Her conclusion that many animals have a concept of death will, in addition to impacting the study of animal minds, have lasting impacts regarding the treatment of animals. If animals understand death the way Monsó has argued they do, through probably the most comprehensive review of cases of animals experiencing death available, we should reconsider the morality of various practices that result in animal deaths in this light. Playing Possum is detailed, funny, and probably the closest a dense philosophical work can get to being called a page turner. Monsó has an impressive ability to recast what it means to understand death, and even the most sceptical reader about animal minds will walk away with a new comprehension of their own relationship to death.

Tiffani Thomason
University of California, Santa Barbara
tthomason@ucsb.edu

Colin Allen
University of California, Santa Barbara
colinallen@ucsb.edu

References

Beck, J. (2012). ‘Do Animals Engage in Conceptual Thought?’, Philosophy Compass, 7, pp. 218–29.

Brosnan, S. F. and Vonk, J. (2019). ‘Nonhuman Primate Responses to Death’, in T. K. Shackelford and V. Zeigler-Hill (eds), Evolutionary Perspectives on Death, Cham: Springer, pp. 77–107.

Fodor, J. A. (1980). The Language of Thought, Cambridge, MA: Harvard University Press.

Sun, F., Wu, Y. E. and Hong, W. (2025). ‘A Neural Basis for Prosocial Behavior toward Unresponsive Individuals’, Science, 387, available at .

Sun, W., Zhang, G.-W., Huang, J. J., Tao, C., Seo, M. B., Tao, H. W. and Zhang, L. I. (2025). ‘Reviving-Like Prosocial Behavior in Response to Unconscious or Dead Conspecifics in Rodents’, Science, 387, available at .