The following is taken from Aleister Crowley’s Magick in Theory and Practice.
Magick is the Science and Art of causing Change to occur in conformity with Will.
(Illustration: It is my Will to inform the World of certain facts within my knowledge. I therefore take “magickal weapons”, pen, ink, and paper I write “incantations”—these sentences—in the “magickal language” ie, that which is understood by the people I wish to instruct I call forth “spirits”, such as printers, publishers, booksellers and so forth and constrain them to convey my message to those people. The composition and distribution of this book is thus an act of Magick by which I cause Changes to take place in conformity with my Will.)
In one sense Magick may be defined as the name given to Science by the vulgar.
ANY required change may be effected by the application of the proper kind and degree of Force in the proper manner, through the proper medium to the proper object.
(Illustration: I wish to prepare an ounce of Chloride of Gold. I must take the right kind of acid, nitro-hydrochloric and no other, in a vessel which will not break, leak or corrode, in such a manner as will not produce undesirable results, with the necessary quantity of Gold: and so forth. Every change has its own conditions.
In the present state of our knowledge and power some changes are not possible in practice we cannot cause eclipses, for instance, or transform lead into tin, or create men from mushrooms. But it is theoretically possible to cause in any object any change of which that object is capable by nature and the conditions are covered by the above postulate.)