Appendix 3.

(453) [Reid and analysis of sensation]

I think that these three events must be distinguished, but that Reid did not sufficiently describe the second (sensation). For him, sensation is simply a modification of the spirit so simple that the only notion we have of it is that of a relationship of the spirit with itself. More accurately, it is merely a different state of the spirit. But my analysis of sensation gives another result.

Sensation is an experience which on analysis always yields three elements: that which experiences; that which causes the experience; the experience itself. I note also that while a thing is indicated through experience relative to the one who experiences, the same thing is indicated through action relative to the agent. This difference in relationship with the one who experiences and the agent enables what is one thing to become two for our mind as a resuslt of the different relationship that the mind adds to it. And this single thing becomes two really different things relative to ther terms to which it is referred. For the one who has the experience, the sensation is entirely different and contrary to that which it is to the agent.

It is now clear that sensation, as passive, is not a means of perceiving a single thing in itself devoid of relationships, but of perceiving it as experience, that is, related solely to the experiencer without reference to the thing's being as action, which is its very own being. In a sensation, the subject receiving the sensation, besides feeling itself, also experiences an event which does not come from itself (the experience it has), but which terminates in some other being as in its cause. It is true that the purely sentient subject does not perceive itself and what acts upon it as totally separate, but this does not prevent us from mentally distinguishing in the sensation: 1. a relationship with the sentient subject as sentient; 2. a relationship terminating not in the sentient subject, but in some other ens different from itself.

We have reserved the word sensation to indicate the sentient subject in so far as it senses, and the phrase sense perception of bodies to indicate sensation itself as a mere experience which, as such, is necessarily related with something extraneous to and different from the sentient subject.
Hence: 1. sense perception of bodies; 2. intellective perception (cf. 417, 418).

As I have said on several occasions, sense perception is subject to the action of our spirit, which takes and envelops bodies themselves. But we cannot say the same of intellective perception, except in so far as sense perception serves as matter for intellective perception.
According to this manner of speaking, Reid's error consisted in distinguishing only three things in the intellective perception of bodies. He should have distinguished four: 1. the mechanical impression on the organs; 2. sensation (considered in its sole relationship with the subject); 3. the sense perception of bodies (that is, our undergoing an experience caused by something outside us); and 4. the intellective perception of bodies (that is, acknowledgement of agents acting on us in a particular mode).

Because he failed to make this precise distinction, Reid confused sense perception of bodies with intellective perception, attributing to the former what applied to the latter. By making intellective perception and sense perception one thing only, he had to deny ideas, which he did not find in sense perception, although he did find the perception of bodies. He concluded therefore that the perception of bodies did not require ideas.

I grant that the sense perception of bodies does not require ideas, but we cannot have the intellective perception of bodies without at least the idea of existence.
Reid would have avoided this error if he had formed a clear idea of the sense perception of bodies. He would have seen that this kind of perception, which lacks anything intellectual, is not sufficient. It is certainly very difficult to form a clear notion of the sense perception of bodies precisely because in this perception we do not perceive bodies as such - we simply perceive them in and with us as terms of our experience, not as agents. Hence, I do not consider the phrase 'sense-perception of bodies' accurate enough, since in this expression 'body' indicates something perceived intellectively. A more accurate expression, even if a little strange, would be 'corporeal sense-perception'.