Diversitas concupiscentiarum naturalium a non naturalibus, non est materialis tantum; sed etiam quodammodo formalis, inquantum procedit ex diversitate obiecti activi, quia obiectum appetitus est bonum apprehensum, unde ad diversitatem activi pertinet diversitas apprehensionis: prout scilicet apprehenditur aliquid ut conveniens absoluta apprehensione, ex qua causantur concupiscentiae naturales, quas philosophus in Rhetoric. vocat irrationales; et prout apprehenditur aliquid cum deliberatione, ex quo causantur concupiscentiae non naturales, quae propter hoc in Rhetoric. dicuntur cum ratione.
The difference between those desires that are natural and those that are not, is not merely a material difference; it is also, in a way, formal, insofar as it arises from a difference in the active object, because the object of the appetite is the apprehended good, and hence diversity of the active [object] follows from diversity of apprehension: either inasmuch as something is [apprehended as] befitting, by absolute apprehension, whence arise natural desires, which the Philosopher calls "non-aspectual" (Rhet. i, 11); or inasmuch as something is apprehended together with deliberation, whence arise those desires that are not natural, and which accordingly the Philosopher calls "aspectual" (Rhet. i, 11).
In homine non solum est ratio universalis, quae pertinet ad partem intellectivam; sed etiam ratio particularis, quae pertinet ad partem sensitivam, ut in primo libro dictum est. Et secundum hoc, etiam concupiscentia quae est cum ratione, potest ad appetitum sensitivum pertinere. Et praeterea appetitus sensitivus potest etiam a ratione universali moveri, mediante imaginatione particulari.
In humans, there is not only universal formal aspect, pertaining to the intellectual faculty; but also particular aspect pertaining to the sensitive faculty (as stated in I, q78, a4; I, q81, a3). Accordingly, even aspectual desire may pertain to the sensitive appetite. Moreover the sensitive appetite can be moved by a universal formal aspect also, through the medium of the particular imagination.