This book traces the modern history of ineffability, the idea that mystical experience lies beyond the reach of language, across twentieth-century scholarship on mysticism. Moving from William James to W.T. Stace and beyond, it examines how theories of ineffability were shaped not only by philosophical commitments but also by rhetorical strategies and disciplinary politics within the academic study of religion. Through close readings of major figures including James, Underhill, Otto, Zaehner, Stace, Smith, Hick, Forman, d’Aquili, and Sells, the book uncovers a crucial historical shift: from early understandings of ineffability as relative, what cannot be fully but can still be partially expressed, to later claims that mystical experience or its source is absolutely ineffable, wholly beyond conceptual mediation. This “absolutization” of ineffability, the book argues, served to defend a perennialist vision of religion’s universal core and to shield it from contextual critique. Concluding with a semiotic “meta-argument” against absolute ineffability, the study proposes that a theory of relative ineffability better accounts for both mystical discourse and ordinary experiences of the unsayable. In doing so, it reorients the study of mysticism toward a more nuanced understanding of how language, experience, and meaning continually shape one another. It is an important read in the study of mysticism. 

Timothy Knepper is Professor of Philosophy at Drake University, where he directs The Comparison Project, a public program dedicated to the exploration of global and comparative religion as well as local, lived religious traditions. His research and teaching span philosophy of religion, mysticism and ineffability, and the intersection of theology, language, and power. He is the author of The Ends of Philosophy of Religion (Palgrave, 2013), Negating Negation: Pseudo-Dionysius and the Christian Apophatic Tradition (Wipf & Stock, 2014), and Philosophies of Religion: A Global and Critical Approach (Bloomsbury, 2022). He has also edited multiple volumes emerging from The Comparison Project’s public dialogues, including Ineffability (Springer, 2017), Death and Dying (Springer, 2019), and Miracles (Springer, 2022). In addition, he has led collaborative works of public scholarship such as A Spectrum of Faith (Drake Community Press, 2017) and Religions of Beijing (Bloomsbury, 2020), both collections of student-authored photo-narratives.

Knepper’s current research focuses on global-critical philosophy of religion, the rhetoric of ineffability, Pseudo-Dionysius the Areopagite, and theodicy as a justification of political and economic systems. He co-founded the Global-Critical Philosophy of Religion Unit of the American Academy of Religion and has received major grants from the Arthur Vining Davis Foundations and the National Endowment for the Humanities to support interfaith engagement and global-critical scholarship.