book reviews 293 Worldviews © koninklijke brill nv, leiden, 2022 | doi:10.1163/15685357-02603012 Michael Marder (with Peter Schuback), Green Mass: The Ecological Theology of St. Hildegard of Bingen. Stanford: Stanford University Press, 2021. pb. $ 24. 167 pp. isbn 978-1-5036-2926-4. I consider this to be one of the—if not the—most significant books of ecothe- ology to have appeared in recent years, despite its apparently historical, and therefore potentially narrow, scope: the ecological theology of the twelfth- century mystic and polymath St. Hildegard of Bingen. Hildegard’s thinking, however, was concerned with the nature of the cosmos, and Green Mass is a book concerned with nothing less than the matter of mattering itself, in particular, with the strange immanence of spirit to matter, with viriditas, the “greenness” which Hildegard saw as both vegetal power of creation and holy spirit. That greenness, that freshness, also shapes the form of Green Mass, which Marder describes as an experiment in “thinking with Hildegard, without the demand to reconstruct anything like her authentic and authoritative thought” (2021: 149). Rather than attempt to explain Hildegard’s many-layered analo- gies between divine spirit and vegetal mattering, Marder seeks to narrate the conditions under which those analogies could be true. The result is a book that is at once faithful to Hildegard’s words (Green Mass is a close reading that cites source texts in detail, and dispenses with footnotes) and promiscu- ous in hermeneutic. Here, Hildegard’s viriditas is braided together with Plo- tinian metaphysics and mystical theology, but also with Marder’s idea of “plant- thinking,” developed in his earlier work: Plant-Thinking: A Philosophy of Vegetal Life (Columbia University Press, 2013), The Philosopher’s Plant: An Intellectual Herbarium (Columbia University Press, 2014), and, with Luce Irigaray, Through Vegetal Being:Two Philosophical Perspectives (Columbia University Press, 2016). Moreover, Marder is not alone in this experiment. As in his past collabora- tion with Irigaray, with which Green Mass shares many thematic if not stylistic concerns, Green Mass is also the result of a dialogue. The musical allusion in the title refers both to the activities of Hildegard as a composer, and to the title of a work by living Swedish composer Peter Schuback, whose scores, together with Schuback’s notes, preface each chapter of the book. Indeed, the seven movements (framed by a prelude and postlude) of Schuback’s Green Mass are adopted as chapter headings by Marder, meaning that each section of the book is a chapter-movement, only complete once it has been experienced in sound (the recordings of Green Mass are available to listen and download at the Stanford University Press website). The immediate effect of this mixed- media co-laboring of author and composer is to expand the notion of what it might mean to sustain viriditas—in particular, what it might mean to sustain it with the freshness the word implies and challenges us to imitate.Where Marder