  The second noteworthy aspect is the insistence of the Stoic theory that the mind of an adult human being is a single, partless item that is rational all the way down. According to the Stoic theory, there are eight parts of the soul, the ‘commanding faculty’ [hêgemonikon] or mind, the five senses, voice and (certain aspects of) reproduction. The mind, which is located at the heart, is a center that controls the other soul-parts as well as the body, and that receives and processes information supplied by the subordinate parts. The minds of non-human animals and of non-adult humans have faculties only of impression and impulse.  Achieving adulthood, for humans, involves gaining assent and reason.  Reason (it would seem) makes assent possible, in that it enables the subject to assent to or withhold assent from impressions, and it transforms mere impressions and mere impulses, such as other animals experience, into rational impressions and rational impulses. The rationality of an impression (for example, of a tree one sees before oneself) consists in its being articulated in terms of concepts, possession of which is constitutive of having reason; the rationality of an impulse consists in the fact that it is generated or constituted by a voluntary act of assent of the mind to a suitable practical (‘impulsive’) impression — the impression, for instance, that something within view would be nice to eat.  Thus, depending on the type of impression assented to, assent generates or constitutes belief (or knowledge) concerning some matter of fact, or an impulse to act in some way or other.