Elaborate philosophical theories have been developed in an attempt to explain the phenomena of mysticism. Thus, in Hindu philosophy, and particularly in the metaphysical system known as the Vedanta, the self or atman in man is identified with the supreme self, or Brahman, of the universe. The apparent separateness and individuality of beings and events are held to be an illusion (Sanskrit maya), or convention of thought and feeling. This illusion can be dispelled through the realization of the essential oneness of atman and Brahman. When the religious initiate has overcome the beginningless ignorance (Sanskrit avidya) upon which depends the apparent separability of subject and object, of self and no self, a mystical state of liberation, or moksha, is attained. The Hindu philosophy of Yoga incorporates perhaps the most complete and rigorous discipline ever designed to transcend the sense of personal identity and to clear the way for an experience of union with the divine self. In China, Confucianism is formalistic and antimystical, but Taoism, as expounded by its traditional founder, the Chinese philosopher Lao-tzu, has a strong mystical emphasis.
The philosophical ideas of the ancient Greeks were predominantly naturalistic and rationalistic, but an element of mysticism found expression in the Orphic and other sacred mysteries. A late Greek movement, Neoplatonism, was based on the philosophy of Plato and also shows the influence of the mystery religions. The Muslim Sufi sect embraces a form of theistic mysticism closely resembling that of the Vedanta. The doctrines of Sufism found their most memorable expression in the symbolic works of the Persian poets Mohammed Shams od-Din, better known as Hafiz, and Jalal al-Din Muhammad Rumi, and in the writings of the Persian al-Ghazali. Mysticism of the pre-Christian period is evidenced in the writings of the Jewish-Hellenistic philosopher Philo Judaeus.
St. Paul was the first great Christian mystic. The New Testament writings best known for their deeply mystical emphasis are Paul's letters and the Gospel of John. Christian mysticism as a system, however, is derived from Neoplatonism through the writings of Dionysius the Areopagite, or Pseudo-Dionysius. The 9th-century Scholastic philosopher John Scotus Erigena translated the works of Pseudo-Dionysius from Greek into Latin and thus introduced the mystical theology of Eastern Christianity into Western Europe, where it was combined with the mysticism of the early Christian prelate and theologian St. Augustine.
In the Middle Ages mysticism was often associated with monasticism. Some of the most celebrated mystics are found among the monks of both the Eastern church and the Western church, particularly the 14th-century Hesychasts of Mount Athos in the former, and Saints Bernard of Clairvaux, Francis of Assisi, and John of the Cross in the latter. The French monastery of Saint Victor, near Paris, was an important center of mystical thought in the 12th century. The renowned mystic and Scholastic philosopher St. Bonaventure was a disciple of the monks of St. Victor. St. Francis, who derived his mysticism directly from the New Testament, without reference to Neoplatonism, remains a dominant figure in modern mysticism. Among the mystics of Holland were Jan van Ruysbroeck and Gerhard Groote, the latter a religious reformer and founder of the monastic order known as the Brothers of the Common Life. Johannes Eckhart, referred to as Meister Eckhart, was the foremost mystic of Germany.
Other important German mystics are Johannes Tauler and Heinrich Suso, followers of Eckhart and members of a group called the Friends of God. One of this group wrote the German Theology that influenced Martin Luther. Prominent later figures include Thomas á Kempis, generally regarded as the author of The Imitation of Christ. English mystics of the 14th and 15th centuries include Margery Kempe and Richard Rolle, Walter Hilton, Julian of Norwich, and the anonymous author of The Cloud of Unknowing, an influential treatise on mystic prayer.
A number of the most distinguished Christian mystics have been women, notably St. Hildegard, St. Catherine of Siena, and St. Teresa of Ávila. The 17th-century French mystic Jeanne Marie Bouvier de la Motte Guyon introduced into France the mystical doctrine of quietism.
By its pursuit of spiritual freedom, sometimes at the expense of theological formulas and ecclesiastical discipline, mysticism may have contributed to the origin of the Reformation, although it inevitably came into conflict with Protestant, as it had with Roman Catholic, religious authorities. The Counter Reformation inspired the Spiritual Exercises of St. Ignatius of Loyola. The Practice of the Presence of God by Brother Lawrence was a classic French work of a somewhat later date. The most notable German Protestant mystics were Jakob Boehme, author of Mysterium Magnum (The Great Mystery), and Kaspar Schwenkfeld. Mysticism finds expression in the theology of many Protestant denominations and is a salient characteristic of such sects as the Anabaptists and the Quakers.
In New England, the famous Congregational divine, Jonathan Edwards, exhibited a strong mystical tendency, and the religious revivals that began in his time and spread throughout the U.S. during the 19th century derived much of their peculiar power from the assumption of mystical principles, great emphasis being placed on heightened feeling as a direct intuition of the will of God. Mysticism manifested itself in England in the works of the 17th-century Cambridge Platonists; in those of the devotional writer William Law, author of the Serious Call to a Devout and Holy Life; and in the art and poetry of William Blake.
The 20th century has experienced a revival of interest in both Christian and non-Christian mysticism. Early commentators of note were the Austrian Roman Catholic Baron Friedrich von Hügel, the British poet and writer Evelyn Underhill, the American Quaker Rufus Jones, the Anglican prelate William Inge, and the German theologian Rudolf Otto. A prominent nonclerical commentator was the American psychologist and philosopher William James in The Varieties of Religious Experience (1902).
In non-Christian traditions, the leading commentator on Zen Buddhism was the Japanese Daisetz Suzuki; on Hinduism, the Indian philosopher Savepalli Radhakrishnan; and on Islam, the British scholar R. A. Nicholson. The last half of the 20th century saw increased interest in Eastern mysticism. The mystical strain in Judaism, which received particular emphasis in the writings of the Cabalists of the Middle Ages and in the movement of the Hasidim of the 18th century, was again pointed up by the modern Austrian philosopher and scholar Martin Buber. Contemporary mystics of note are the French social philosopher Simone Weil, the French philosopher Pierre Teilhard de Chardin, and the American Trappist monk Thomas Merton.