Within the modern system of Thelema, developed by occultist Aleister Crowley in the first half of the 20th century, Thelemic mysticism is a complex mystical path designed to do two interrelated things: to learn one's unique True Will and to achieve union with the All. The set of techniques for doing so falls under Crowley's term Magick, which draws upon various existing disciplines and mystical models, including Yoga, Western ceremonial ritual (especially invocations and eucharistic ceremony), the Qabalah, and several divination systems, especially the tarot and astrology.