ON SENSE AND THE SENSIBLE

London. British Museum. Additional MS 8786.

(Chapter One: Concerning the Organs of Sensing)

ALTHOUGH the study of all animal parts has been generally established f. 62 a 1.

in the book On Animals in regard to their physical composition, and
it was established in the book On the Soul regarding the organs of sensing
and their objects in regard to their transformation, it is not redundant
to determine their origin in this book, On Sense and the Sensible,
specifically in relation to the four elements and in themselves.

In the 19th book of On Animals, the work of sensing is attributed to
the spirits: subtle, vaporous substances thought to flow through the nerves to facilitate bodily functions original: "spiritibus". This is also found in the second book of Perspective, the second book of Avicenna's On the Soul, the book On the Difference Between Spirit and Soul, and many other places. But it should not be understood that the spirit is the organ and instrument of the soul in the sense that the soul perfects: brings to its full or completed state of being original: "perficiatur" the spirit. Rather, the spirit is the medium through which the sensitive soul operates. The soul alone and immediately completes the organic body and its parts, which belong to its own substance. This is shown at the end of the Metaphysics through the principle that accidental form: a non-essential property, like color or surface shape original: "forma accidentalis" completes its matter immediately: a surface completes a body, and color completes a surface. Therefore, it is even more true that a substantial form: the essential nature that makes a thing what it is original: "forma substantialis" completes its matter immediately. Thus, the soul completes its matter, namely the organic body, immediately and without the spirit. This is because the spirit is not part of the body's substance, even though it is within the body like the humors: the four vital fluids of the body, such as blood and bile original: "humores" and other such things, which are distinct from the body's substance at their boundaries. Natural heat should be understood in the same way. It is even less of an instrument or organ of the soul, although Aristotle and the Commentator: the philosopher Averroes, whose commentaries on Aristotle were central to medieval study original: "Commentatore" often call it an organ and instrument.

Since all the authors mentioned above and others maintain that the sensible powers originate in the nerves and the flesh, a difficulty arises. When Aristotle denies sensation to the nerves in the first book of On the Soul, it will seem to someone that the nerves are only vessels containing the instruments. In these instruments, the powers exist as if in a subject which...