James identifies four marks of mystical states. The first and most obvious is ineffability: the experience cannot be adequately described in words — it must be felt directly, as music must be heard. The second is noetic quality: mystical states feel like states of knowledge, not merely feeling. They disclose depths of truth that ordinary discursive intellect cannot reach. Transiency and passivity complete the picture: the states do not last, and they are received rather than constructed.
James traces mysticism from its humblest forms — the deepened sense of meaning in a familiar phrase, the feeling of "having been here before" — to its most extreme expressions in the Sufi poets, Teresa of Ávila, and the Upanishadic tradition. He refuses to restrict the category to explicitly religious contexts: natural mysticism (Wordsworth's spots of time, Whitman's cosmic moments) and drug-induced states (nitrous oxide, chloroform) produce experiences with the same formal marks.
James's verdict is carefully calibrated. Mystical states are authoritative for those who have them — they carry a conviction that argument cannot shake. But they establish no doctrine for those who have not had them: the content of different mystics' experiences is too various and inconsistent to ground any single theology. What they do establish, for James, is that the normal waking consciousness is surrounded by a wider field of experience from which religious feeling draws — "something more" than ordinary life offers.
Mysticism is the subject of Lectures XVI and XVII of The Varieties (1902). James's four marks — ineffability, noetic quality, transiency, passivity — have become standard in the philosophy of mysticism. The account of nitrous-oxide mysticism appears in the 1882 paper "Subjective Effects of Nitrous Oxide."
