what is visible in itself. Such is the relationship between colour and body: colour is visible in itself, whereas a body is visible by virtue of its colour. Thus, whatever has no colour cannot be seen. If a thing were seen solely because it exists, sounds and all other objects of the five senses would necessarily be visible. Sight, hearing, and the rest of the five senses would then be a single sense. All this runs contrary to reason.

This question and others like it have forced the speculative theologians to concede that colours can be heard and sounds can be seen. All this departs from nature and from what human reason can comprehend. For it is evident that the sense of sight differs from the sense of hearing, that what one perceives differs from what the other perceives, and that the organ of one differs from the organ of the other. Sight cannot turn into hearing, just as it is impossible