The Core of 'Book Four'

Magick in Theory and Practice is the central instructional volume of Aleister Crowley's magical system, forming the third part of the larger work known as Book Four (Liber ABA); this part was first published in Paris in 1929-30. It presents his general theory of "Magick", spelled with a k to distinguish it from stage conjuring, famously defined as "the Science and Art of causing Change to occur in conformity with Will," a deliberately broad definition under which every intentional act becomes magical.

The book covers the practical disciplines in turn: banishing, consecration, invocation and evocation, the use of the ritual weapons, divination, and the training of the will and the body, all organised around the Thelemic axiom that the aim of magick is to discover and carry out one's "True Will." Written with Crowley's characteristic mixture of technical precision, erudition and provocation, it remains the most systematic single statement of his practical method and one of the most influential magical manuals of the twentieth century.