There are certain common fallacies current about mysticism: that mystics are not practical and that they are revolutionary; on the contrary, many of the greatest mystics have been both intensely active as well as submissive to authority of whatever sort. Nor is the solitary thinker necessarily, or even usually, a mystic. There is no accepted explanation of mysticism, and few psychologists have interested themselves in its practice. William James studied the nature of mysticism but reached no conclusion that satisfied him. A significant philosophical evaluation of mysticism was made by Henri Bergson.

There are two general tendencies in the speculation of mystics—to regard God as outside the soul, which rises to its God by successive stages, or to regard God as dwelling within the soul and to be found by delving deeper into one's own reality. The idea of transcendence, as held most firmly by mystics, is the kernel of the ancient mystical system, Neoplatonism, and of Gnosticism. Their explanation of the connection between God and humans by emanation is epoch-making in the philosophy of contemplation. Among those who think of God, or the Supreme Reality, as being within the soul are the Quakers (see Friends, Religious Society of) and the adherents of Vedanta.

The language of mysticism is always difficult and usually symbolic. This is readily seen in the Song of Songs in the Old Testament, in the book of Revelation in the New Testament, and in the writings of William Blake. Mystics, especially those of the Roman Catholic and the Islamic traditions, have made use of a terminology borrowed from ordinary human love. A conventional analysis is as follows: The soul undergoes a purification (the purgative way), which leads to a feeling of illumination and greater love of God (the illuminative way); after a period the soul may be said to enter into mystical union with God (the unitive way), which begins with the consciousness that God is present to the soul; the soul progresses through a time of quiet and an ecstatic state to a final perfect state of union with God (spiritual marriage). Late in this process there is an experience (the dark night of the soul) wherein the contemplative finds himself completely deserted by God, by hope, and, indeed, even by the power to pray; it lasts sometimes for years.

Visions, voices, ecstasies may accompany any or none of the states of contemplation before the final union. It is because of these external and nonessential manifestations that the erroneous idea has arisen that all enthusiastic and nonintellectual religious movements are necessarily mystical. The positive convictions of the mystic arise from the fact that they are based on what he or she must regard as objective reality directly perceived.

Among the principal contemplatives of Christianity from post-Apostolic times to the Reformation are Clement of Alexandria, Origen, St. Augustine, the false Dionysius the Areopagite, Cassian, St. Gregory I, Erigena, St. Peter Damian, St. Anselm, St. Bernard of Clairvaux, Hildegard of Bingen, Joachim of Fiore, Richard of Saint Victor, Hugh of Saint Victor, Hadewijch, St. Gertrude, St. Francis, Jacopone da Todi, St. Bonaventure, St. Thomas Aquinas, Ramon Lull, Dante, Eckhart, Tauler, Suso, Ruysbroeck, Groote, Thomas à Kempis, Nicholas of Cusa, Rolle of Hampole, Walter Hilton, Juliana of Norwich, Margery Kempe, St. Bridget of Sweden, St. Catherine of Siena, Gerson, St. Bernardine of Siena, and St. Joan of Arc. The Catholic tradition was continued by St. Ignatius of Loyola, St. Theresa of Ávila, St. John of the Cross, St. Francis de Sales, and St. Theresa of Lisieux. Orders that have given their name to types of mysticism are Carmelites, Carthusians, and Cistercians.

Among great Protestant mystics are Jakob Boehme and George Fox, founder of Quakerism, the foremost Protestant mystical movement. In the 17th and 18th cent. much literature of the contemplative life was written by the metaphysical poets and by Henry More, William Law, and others. Extremes in post-Reformation mysticism are seen in Jansenism (see under Jansen, Cornelis) and in quietism; and Emanuel Swedenborg may be regarded as a Protestant mystic. Also included in the mystic tradition were the Hermetic philosophers and the Alchemists.

In Judaism the mystical tradition represented by the kabbalah was continued in the modern Hasidism. For Islamic mysticism, see Sufism; al-Ghazali; Farid ad-Din Attar; Jalal ad-Din Rumi; Muin ad-Din Hasan Chishti; Hafiz; Jami; Sadi. For Hindu mysticism, see Vedanta; yoga; Aurobindo Ghose; Chinmoy Ghose; Dayananda Saraswati; Ramakrishna; Vivekananda; Yogananda. For Buddhism, see Zen Buddhism; Buddha; Milarepa; Daisetz Suzuki. See also Taoism.