The contemporary academic study of religion has its roots in conceptual and theoretical structures developed in the early to mid-20th century. A particularly important example of such a structure is the concept of the “numinous” developed by the theologian and comparativist Rudolf Otto (1869–1397) in his work, The Idea of the Holy: An Inquiry into the Non-Rational Factor in the Idea of the Divine and its Relation to the Rational (1923). Building on the work of Immanuel Kant (1724–1804), Friedrich Schleiermacher (1772–1834), and Jakob Fries (1773–1843), Otto developed the concept of the numinous—a “category of value” and a “state of mind”—as a way to express what he viewed as the “non-rational” aspects of the holy or sacred that are foundational to religious experience in particular and the lived religious life in general. For Otto, the numinous can be understood to be the experience of a mysterious terror and awe (Mysterium tremendum et fascinans) and majesty (Majestas) in the presence of that which is “entirely other” (das ganz Andere) and thus incapable of being expressed directly through human language and other media. Otto conceives of the concept of the numinous as a derivative of the Latin numen, meaning “spirit,” etymologically derived from the concept of divine will and represented by a “nodding” of the head. Otto argues that understanding the numinous in a satisfactory way requires a scholar to draw upon their own experience of religious sentiments, given its non-discursive and direct nature; this becomes a point of contention among later secular scholars of religion. In later works, such as Mysticism East and West: A Comparative Analysis of the Nature of Mysticism (1932), Otto gives numerous examples of the ways in which the concept of the numinous can be applied cross-culturally to traditions beyond Christianity, such as Hinduism and Buddhism. Otto’s theories regarding the numinous have been extremely influential in the development of the academic study of religion in the 20th and 21st centuries, as evidenced by the impact they had upon scholars such as Carl Jung, Mircea Eliade, and Ninian Smart, whose works were instrumental in the formation of religious studies as a discipline. Jung cites the concept of the numinous extensively with regard to his theories on the breakthrough of unconscious material into conscious awareness. Eliade’s work The Sacred and Profane: The Nature of Religion (1959) takes Otto’s concept of the numinous as a starting point in the development of its own theory; Eliade’s use of the category of the “sacred” might be considered derivative of Otto’s larger conception of the “holy” (das Heilige). Eliade’s work, like Otto’s, has been extensively criticized for postulating a sui generis nature of both the numinous and the sacred, which are viewed by Eliade as irreducible to other phenomena (historical, political, psychological, and so forth). Smart’s influential “dimensional analysis” theory and his scholarship on the topic of world religions is highly informed by his utilization of Otto’s theory of the numinous within the contexts of his cross-cultural reflections on religion and the development of his “two-pole” theory of religious experience. The concept of the numinous continues to be theorized about and applied in contemporary academic research in religious studies and utilized as part of a framework for understanding religion in university courses on world religions and other topics in the academic study of religion. In part through the work of Eliade, Smart, and other scholars—Otto included—who have found a popular readership, the term has been disseminated to such a degree as to find common usage in the English language and popular discourse.
The comparative study of mysticism began in the mid-19th century, with the development of the modern meaning of the word, which had begun to be used as a substantive, with the classification of “mystics” in the 17th century. This differed from the traditional Greek Christian use of the adjective mystikos, to qualify rituals, scriptures, sacraments, and theology as “mystical” contexts of the human encounter with the Divine. This modern shift highlighted the personal experience of ultimate Reality, rather than the sociocultural context. Certain individuals claimed to encounter the Divine or spiritual realities more directly, separate from traditional mediums of religious experience. The study of this phenomenon tended in the early 20th century to focus on the psychology and the phenomenology of the personal experience, generally described as an altered state of consciousness with specific characteristics, processes, stages, effects, and stimulants. This emphasis on common features influenced the development of perennialist and traditionalist theorists, who saw evidence of the same experiential origin, fundamental principles, or epistemology among major world religions. Some essentialist views of mysticism argued that a pure consciousness-experience of undifferentiated unity or non-duality is the core feature of all mysticism, in contrast to other religious experiences. Reaction to these positions led to contextualist or constructivist views of mysticism, which presume the sociocultural character of mysticism. In its most extreme form, the contextualist perspective suggests that all mystical experiences among traditions are different, given diverse socio-religious categories that overdetermine the experience. In turn, some critical scholarship has proposed qualifications to contextualism within the context of a general acceptance of many of its tenets, even among many theorists with essentialist tendencies. Up to the late 20th century, much scholarship in the area tended to downplay the sociocultural features of mysticism, emphasizing the psychological dynamics and an individual, disembodied, and radically transcendent ideal. This brought into question the relationship of morality to mystical experience and raised concerns about the status of entheogens—the use of psychoactive drugs in religious contexts. Interest in the comparative study of mysticism has also extended into the area of neuroscience, where researchers explore electro-chemical brain states associated with mystical experience, in proposing evidence of a mystical neurological substrate. But the essentialist/contextualist debate also moved the comparative study of mysticism beyond issues of epistemology, consciousness-states, ontology, and cognitive neuroscience, broadening the field to include other aspects of religious experience. Some studies have brought feminist concerns to bear on the discussion, insofar as women’s mysticism has been overshadowed and even repressed by men, and was seen to preclude legitimate experiential possibilities of a more embodied character. Related scholarship in history and depth psychology has focused creatively on the nature and significance of erotic elements of mysticism in comparative studies, with special attention to associated physical phenomena and their transformative dynamics. Similarly, more embodied features of comparative mysticism are the subject of transpersonal psychology, which draws on many humanistic disciplines and supports participatory approaches to the field. Transpersonal psychology remains open to claims that the ego can be transcended in movements into higher states of being that ideally involve personal/spiritual enhancement and integration. Also, some more recent proponents of new comparative theology advocate methods that engage the scholar in specific beliefs or practices of another tradition, and include subsequent clarification and elaboration of one’s own perspective in light of such comparative study, in exploring phenomena related to comparative mystical experience.