This classroom-friendly book, written by a prominent historian of religions, offers reflections on the central theoretical object in the academic study of religion. It does not explicitly ask or answer any traditional philosophical questions. Nevertheless, I judge that there are two ways that philosophers of religion should engage with the project this book represents.

Here is a quick summary of the book's five chapters. The first, ‘What Religion Is’, considers the difficulties of defining the term ‘religion’ and spells out the desiderata of any good definition. Tweed argues that the most useful definition of ‘religion’ will be one that is based not solely on some distinctive content (such as supernatural forces) nor solely on a distinctive function (such as orienting people in time), but rather ‘a both/and definition’ that describes content and function (11). To emphasize that any particular religion is always a historical entity, ‘a process rather than a thing’, Tweed uses aquatic rather than locative metaphors: religions here are ‘confluences of organic-cultural flows’ (12, 13). The second chapter, ‘What Religion Does’, discusses a wide range of ways in which religions function to provide meaning and to exert social power. Tweed focuses especially on the ways in which religious participation forms social bonds, creates collective identity, and provides spatial and temporal orientation. This lets him speak of religion as akin to an ecological-cultural niche or habitat, and then to explore how such habitats can become stressed, cracked, or unsustainable. Chapter 3, ‘How Religion is Expressed’, pulls the focus away from the notion that the heart of religion is some direct, unmediated experience. In an analysis that reminded me of the work of Ninian Smart, Tweed maps out eight ‘modes’ in which religion is found in the world. On this well-rounded picture, religion informs how people experience the world through their senses, how they imagine it symbolically and analogically, how they make their food and clothes and architecture, how they narrate their stories and literature, how they conceptualize their doctrines and philosophies, how they enact their legal and ethical rules, how they perform their rituals and ceremonies, and how they gather in and create social structures.

The last two chapters of the book are both historical. Chapter 4, ‘How Religion has Changed’, gives a breakneck survey of the ways in which religious forms of life have varied – from the emergence of ‘foraging religion’ among early human beings tens of thousands of years ago, to ‘farming religion’ when agriculture began, to the religion of ancient empires (Egyptian, Mesopotamian, Harappan, and Chinese) and then medieval and modern empires, and then to ‘industrial religion’. Tweed's style of modifying the term ‘religion’ in terms of the kind of labour and politics of the era helpfully underlines his point that the term ‘religion’ names not a Platonic form but rather a historical structure that varies according to the lifeworld of those who create it. Chapter 5, ‘Global Religion Today’, surveys the expressions of religion in the twentieth century, especially since the Second World War. This chapter presents religion today as a unifying force, building bridges between communities, and also as a fragmenting force, feeding animosities and violence. As in the previous chapters, Tweed presents religion as shaped by the ‘lifeway transitions’ (89) of work and technology, here moving from the global spread of industrialization and its ‘factory religion’ to the demands of the information age, the service economy, and climate emergencies. Every part of this book is pitched at a level where college students can catch it, and there are illuminating examples throughout.

I mentioned that I think that in two ways philosophers of religion should engage with the project of this book. In the first place, I think that we should adopt a view of our object of study that is as rich as the one Tweed gives us. How common it is to see philosophers of religion zero in on a decontextualized claim or text with no appreciation of the religious practices its author engaged in – let alone the legal, economic, political, or architectural structures that shaped its author's life. Adopting an account of religion that is as multifaceted as the one in this book would help to re-racinate those claims and texts in the historical soil from which they grew.

In the second place, I think that philosophers of religion should see the analysis of ‘what religion is’ and ‘what religion does’ not as the purview of historians and anthropologists but as a responsibility that belongs also to philosophers. It is not possible to give an account of religion without at least implicitly answering questions that are ontological, epistemological, or axiological. This book provides two nice examples of places where philosophy could help.

In the first place, the way in which ‘religion’ gets defined raises several questions. Tweed writes that the best definition of ‘religion’ will describe not only its function in people's lives but also some distinctive kind of entity as the content of its concept. I think this is entirely right. But his treatment of the content of ‘religion’ is wobbly. At some points, he describes this content as ‘suprahuman forces’ (which would include hurricanes, I think) and at others he describes it as ‘supernatural forces’ (which would not). He sometimes also includes in his definition the phrase ‘or human forces’ (which would then exclude very little). At one point, he recognizes that the borders he has drawn are blurry and so he adds that these forces must also be ‘ultimate’ (15). ‘Ultimacy’ had not been part of his definition at the outset, and adding it involves a shift from certain kinds of entities to their role in one's life, that is, from content back to function. Tweed's shorthand for his definition (‘religion as wonder and worry’, 11) also drops content to focus on function. Moreover, Tweed's definition sometimes seems monothetic and sometimes polythetic. And here is a crucial issue that needs much more discussion: I judge that one's assessment of how best to define ‘religion’ turns not on which definition successfully captures the reality of religion, but instead on one's purpose. As Tweed says, what we want is not a definition that is true but one that is useful. If this is right, then it follows that one cannot criticize a definition for leaving out something that ‘really is’ religious, a point that scholars may forget. And more importantly, this insight about the pragmatics of definitions raises the question of what a good definition of ‘religion’ is supposed to be useful for. That is, what is the purpose of the study of religion? This reflexive question about the aims of education is one that philosophers of religion should care about.

A second place in the study of the concept ‘religion’ where philosophy is needed has to do with the relation between religious subjectivity and the material world. Tweed has a chapter that outlines the eight modes in which religion is ‘expressed’. That verb treats the material world – even one's body, even one's neurons – as a ‘conduit’ through which religious ideas get from people's minds out into the world (45, 38). Though Tweed seeks to escape old dualisms, this language fails to credit the agency of material objects or the contribution of the body to religious thought. Relatedly, some scholars of religion like Talal Asad and Saba Mahmood have followed Michel Foucault in arguing that one should ‘reverse’ this inside-to-out view so that one studies not how a religious culture is the expression of people's beliefs and desires but instead how religious subjects are produced through the disciplinary effects of rituals and other social structures. From this post-structuralist perspective, the notion that culture is an expression of what people believe and desire reflects a Protestant perspective we should move beyond. My point is not that the post-structuralists are right about the relation of material structures and religious subjectivity. (For a smart defence of the language of ‘expression’, see Molly Farneth, The Politics of Ritual (2021).) My point is simply that the academic study of religions requires scholars to answer questions about cognition, agency, embodiment, personhood, and intentionality, and this is a list of questions that would benefit from philosophical attention. Philosophy of religion, in other words, should include the philosophy of religious studies. Thomas Tweed has been a historian of Cuban Catholics and Buddhist immigrants, but in this book he reaches above any particular empirical example to think about what everyone in our interdisciplinary field has in common. Philosophers of religion should meet him there.