In The Varieties of Religious Experience (1902), William James proposed that mystical states are ineffable, defying expression; noetic, carrying a sense of insight and authority; transient, rarely lasting long; and passive, felt as if the will were held by a superior power. His four marks remain the starting point of much discussion.
Four Marks of Mysticism
William James’s criteria for mystical states: ineffability, noetic quality, transiency and passivity.
Also: William James’s marks