According to Peter Moore, the term "mysticism" is "problematic but indispensable."[10] It is a generic term which joins together into one concept separate practices and ideas which developed separately,[10] According to Dupré, "mysticism" has been defined in many ways,[11] and Merkur notes that the definition, or meaning, of the term "mysticism" has changed through the ages.[web 1] Moore further notes that the term "mysticism" has become a popular label for "anything nebulous, esoteric, occult, or supernatural."[10]

Parsons warns that "what might at times seem to be a straightforward phenomenon exhibiting an unambiguous commonality has become, at least within the academic study of religion, opaque and controversial on multiple levels".[12] Because of its Christian overtones, and the lack of similar terms in other cultures, some scholars regard the term "mysticism" to be inadequate as a useful descriptive term.[10] Other scholars regard the term to be an inauthentic fabrication,[10][web 1] the "product of post-Enlightenment universalism."[10]

Union with the Divine or Absolute and mystical experience
See also: Hesychasm, Contemplative prayer, and Apophatic theology
Deriving from Neo-Platonism and Henosis, mysticism is popularly known as union with God or the Absolute.[13][14] In the 13th century the term unio mystica came to be used to refer to the "spiritual marriage," the ecstasy, or rapture, that was experienced when prayer was used "to contemplate both God’s omnipresence in the world and God in his essence."[web 1] In the 19th century, under the influence of Romanticism, this "union" was interpreted as a "religious experience," which provides certainty about God or a transcendental reality.[web 1][note 1]

An influential proponent of this understanding was William James (1842–1910), who stated that "in mystic states we both become one with the Absolute and we become aware of our oneness."[16] William James popularized this use of the term "religious experience"[note 2] in his The Varieties of Religious Experience,[18][19][web 2] contributing to the interpretation of mysticism as a distinctive experience, comparable to sensory experiences.[20][web 2] Religious experiences belonged to the "personal religion,"[21] which he considered to be "more fundamental than either theology or ecclesiasticism".[21] He gave a Perennialist interpretation to religious experience, stating that this kind of experience is ultimately uniform in various traditions.[note 3]

McGinn notes that the term unio mystica, although it has Christian origins, is primarily a modern expression.[22] McGinn argues that "presence" is more accurate than "union", since not all mystics spoke of union with God, and since many visions and miracles were not necessarily related to union. He also argues that we should speak of "consciousness" of God's presence, rather than of "experience", since mystical activity is not simply about the sensation of God as an external object, but more broadly about "new ways of knowing and loving based on states of awareness in which God becomes present in our inner acts."[23]

However, the idea of "union" does not work in all contexts. For example, in Advaita Vedanta, there is only one reality (Brahman) and therefore nothing other than reality to unite with it—Brahman in each person (atman) has always in fact been identical to Brahman all along. Dan Merkur also notes that union with God or the Absolute is a too limited definition, since there are also traditions which aim not at a sense of unity, but of nothingness, such as Pseudo-Dionysius the Areopagite and Meister Eckhart.[web 1] According to Merkur, Kabbala and Buddhism also emphasize nothingness.[web 1] Blakemore and Jennett note that "definitions of mysticism [...] are often imprecise." They further note that this kind of interpretation and definition is a recent development which has become the standard definition and understanding.[web 6][note 4]

According to Gelman, "A unitive experience involves a phenomenological de-emphasis, blurring, or eradication of multiplicity, where the cognitive significance of the experience is deemed to lie precisely in that phenomenological feature".[web 2][note 5]

Religious ecstasies and interpretative context
Main articles: Religious ecstasy, Altered state of consciousness, Cognitive science of religion, Neurotheology, and Attribution (psychology)
Mysticism involves an explanatory context, which provides meaning for so-called mystical and visionary experiences, and related experiences like trances. According to Dan Merkur, mysticism may relate to any kind of ecstasy or altered state of consciousness, and the ideas and explanations related to them.[web 1][note 6] Parsons stresses the importance of distinguishing between temporary experiences and mysticism as a process, which is embodied within a "religious matrix" of texts and practices.[26][note 7] Richard Jones does the same.[27] Peter Moore notes that mystical experience may also happen in a spontaneous and natural way, to people who are not committed to any religious tradition. These experiences are not necessarily interpreted in a religious framework.[28] Ann Taves asks by which processes experiences are set apart and deemed religious or mystical.[29]

Intuitive insight and enlightenment
Main articles: Enlightenment (spiritual), Divine illumination, and Subitism
Some authors emphasize that mystical experience involves intuitive understanding of the meaning of existence and of hidden truths, and the resolution of life problems. According to Larson, "mystical experience is an intuitive understanding and realization of the meaning of existence."[30][note 8] According to McClenon, mysticism is "the doctrine that special mental states or events allow an understanding of ultimate truths."[web 7][note 9] According to James R. Horne, mystical illumination is "a central visionary experience [...] that results in the resolution of a personal or religious problem.[3][note 10]

According to Evelyn Underhill, illumination is a generic English term for the phenomenon of mysticism. The term illumination is derived from the Latin illuminatio, applied to Christian prayer in the 15th century.[31] Comparable Asian terms are bodhi, kensho and satori in Buddhism, commonly translated as "enlightenment", and vipassana, which all point to cognitive processes of intuition and comprehension. According to Wright, the use of the western word enlightenment is based on the supposed resemblance of bodhi with Aufklärung, the independent use of reason to gain insight into the true nature of our world, and there are more resemblances with Romanticism than with the Enlightenment: the emphasis on feeling, on intuitive insight, on a true essence beyond the world of appearances.[32]

Spiritual life and re-formation
Main articles: Spirituality, Spiritual development, Self-realization, and Ego death
Other authors point out that mysticism involves more than "mystical experience." According to Gellmann, the ultimate goal of mysticism is human transformation, not just experiencing mystical or visionary states.[web 2][note 13][note 14] According to McGinn, personal transformation is the essential criterion to determine the authenticity of Christian mysticism.[23][note 15]