Magick, Liber ABA, Book 4 is a book by 20th-century occultist Aleister Crowley. It is widely considered to be his magnum opus.Magick is a lengthy treatise on ceremonial magic (which he anachronistically refers to as 'magick'), synthesised from many sources including yoga, Hermeticism, medieval grimoires, contemporary magical theories from writers like Eliphas Levi and Helena Blavatsky, and his own original contributions. It consists of four parts: Mysticism, Magick (Elementary Theory), Magick in Theory and Practice, and ΘΕΛΗΜΑ—the Law (The Equinox of The Gods). It also includes numerous appendices presenting many rituals and explicatory papers. Liber ABA refers to this work being a part of Crowley's system of magical works known as libri (Latin for 'books'). In most systems such as gematria where letters are given numerical value, ABA adds up to 4, a number which represents the Four Elements, Stability and so on (thus the name Book 4). Source: Wikipedia (en)