The opening section lays out Thomas Aquinas? arguments for rejecting the interpretations of the active intellect put forth by Avicenna and Averroes. The interpretation of how intelligible species are formed focuses on the thesis that the foundation of Aquinas? theory of active intellect?s abstraction lies in his metaphysical assertion of the real composition of essence and being. The text demonstrates the validity of Geach?s critique of ?abstractionism? in the interpretations of the Aquinas? theory of active intellect?s abstraction. Active intellect actually imparts its own form onto the content of the phantasms, that is the active intellect transfers the phantasm an intelligible mode of being. The final section examines the roles of the active intellect and phantasms as the principal and instrumental causes of intelligible species, respectively.