Opus Majus of Roger Bacon, Vol. II (Burke English trans.)

a sense, because it is in truth a sense, and a sensitive faculty. The statement, therefore, that qualities belonging to complexions are not apprehended by a sense must be understood as applying to a special sense, the common sense, and imagination; but they can readily be apprehended by estimation, which, although not called a sense, is, however, a part of the sensitive soul.

But estimation does not retain a form, although it receives it like the common sense, and it therefore requires another faculty in the remotest part of the posterior cell Medieval anatomy placed the faculties in three "cells" or ventricles of the brain to retain forms coming to the estimative faculty and to be its storehouse and repository, just as imagination is the storehouse of the common sense. This is the memorative faculty, as Avicenna states in the first book On the Soul. Cogitation or the cogitative faculty is in the middle cell and is the mistress of the sensitive faculties. It takes the place of reason in brutes, and is therefore called the logical—that is, the rational—faculty, not because it employs reason, but because it is the ultimate perfection of brutes, just as reason is in man, and because the rational soul in man is united directly with it. By this faculty the spider weaves its geometrical web, the bee makes its hexagonal house—choosing one of the figures that fill out space—and the swallow its nest. The same is true of all the works of brutes that are similar to human art. Man by means of this faculty sees wonderful things in dreams, and all the faculties both posterior and anterior of the sensitive soul serve and obey it, because they all exist on account of it. For the forms or species that are in the imagination multiply themselves into the cogitative faculty, although they exist in the imagination according to their nature primarily because of phantasia i.e., power of imagination, which uses those forms; but the cogitative faculty holds those forms in a nobler way, and the forms of the estimative and memorative faculties exist in the cogitative faculty in accordance with a nature nobler than that existing in those faculties, and therefore the cogitative faculty uses all the other faculties as its instruments. In man there is in addition, from without and from creation, the rational soul, which is united with the cogitative faculty primarily and immediately, and uses this faculty chiefly as its own special instrument. Species i.e., mental images are formed in the rational soul by this faculty. Wherefore when this faculty is impaired the judgment of reason is especially perverted, and when it is in a healthy condition the intellect functions in a sound and rational way.