Origins of the Medieval Theory That Sensation Is an Immaterial Reception of a Form
Martin M. Tweedale (UNiversity of Alberta)
Philosophical Topics, Vol. 20, No. 2, Fall (1992)
Ten years ago Sheldon M. Cohen noticed a problem in Aquinas’s theory of sense perception which had gone unremarked because of a misunderstanding as to what Aquinas meant by saying that the senses receive the form of the sense object without the matter, Aquinas, of course, had taken the phrase directly from Aristotle’s De anima II, 12, and I shall have something to say later about what Aristotle himself intended; for the moment, I want to concentrate on Aquinas. Cohen pointed out that many recent interpreters took Aquinas to mean that the sensible form comes to have an existence in the soul itself rather than in any sense organ and that the sensible form so existing is a mental image that has no physical existence.
Cohen claimed this interpretation was refuted by Aquinas’s own texts. Aquinas clearly held, Cohen argued, that the sensible form when received by the sense exists in the sense organ, not in the sensitive soul per se, even though it exists in that organ “spiritually” or “intentionally”. The force of saying that the form has an “immaterial” existence in the organ is to distinguish its mode of existence there from its mode of existence in some material thing that possesses the sensible quality in question. When the sensible form of whiteness exists immaterially in the eye or pupil it does not make that bit of anatomy white, but rather exists there somehow without qualitatively changing the eye. Cohen suggested that Aquinas may have thought of this mode of existence as like that of mirror images. What is in the pupil is a reflection of the color of some external object. When a white image is in a mirror the mirror is not itself white.