The Opus Majus of Roger Bacon

Therefore, there is something there sensibly beyond the twenty-nine aforementioned things, and beyond those which are reduced to them. For there must be something more active and capable of altering the sensing body than light and color, because it induces not only comprehension, but an affection of fear, or love, or flight, or delay. And this is the quality of the constitution original: "complexionis" of any thing by which it is assimilated to others in a special or general nature, through which they are mutually in agreement, comforted, and invigorated, or through which they differ, are opposed, and mutually become harmful to one another. Hence, not only do light and color create their species original: "species" — here meaning visible images or sensible forms and virtues, but far more so do constitutional qualities; indeed, the very substantial natures of things, whether agreeing with or contrary to one another, create powerful species that strongly alter the sensitive soul so that it is moved by affections of fear, horror, and flight, or their opposites. And these species or virtues coming from things, although they change and alter the particular senses, the common sense, and the imagination, just as they do the air through which they pass, nonetheless no virtue of the soul judges concerning these. Instead, there must be a virtue of the sensitive soul that is far more noble and powerful, and this is called estimation original: "aestimatio" or the estimative faculty, as Avicenna says in the first book of De Anima On the Soul, which he says perceives non-sensible forms concerning sensible matter. Sensible matter is called here that which is known by the particular senses and the common sense, as are the twenty-nine things mentioned above. And a non-sensible form is called that which is not perceived by those senses in themselves, because they are commonly called senses, even though other virtues of the sensitive soul could equally well be called senses, if we wished to call them so, since they are parts of the sensitive soul. For every part of the sensitive soul can be called a sense, because in truth it is a sense and a sensitive virtue. Therefore, what is said—that constitutional qualities 1 are not sensed by sense—must be understood as meaning by the particular and common sense and the imagination; but they can certainly be sensed by the estimation, which, although it is not called a sense, is nonetheless a part of the sensitive soul.

Animals have an organ of

But the estimation does not retain the species, although it receives it like the common sense, and therefore it needs another virtue in the final part

1 Constitutional qualities, as given in the Magdeburg manuscript, seems better than "substances," the reading of the other manuscripts.