 The intellectual faculty, i.e., the intellect, comprises a passive capacity—the possible intellect—and an active capacity—the agent intellect, which is the intrinsic active principle of the act of intellection (In De an.: q.13). The proper operation of the passive capacity is apprehension, i.e., the assimilation of quiddities through the reception of intelligible forms. In turn, the proper operation of the active capacity is abstraction, i.e., the production of intelligible forms which trigger the operation of the possible intellect (In De an.: q.13).