The psychological characteristics of the five senses in general, omitting those which properly belong to physiological inquiries, may be summed up as follows: The proper function of each and all of them is a sensation, or affection of the nervous organism as animated; which affection, however, does not, and in all probability cannot, exist in consciousness without an accompanying intellectual cognition of the same organism as extended or occupying space.
This cognition (the perception proper) is referred to the intellect rather than to the sense, chiefly for two reasons: Firstly, because it is not, like the sensation proper, limited in each case to a single form of sensibility, but appears as the common condition of consciousness in all. Secondly, because it is not in many cases the consciousness of a single object as such, but of a relation, either between the parts of the sensible object, viewed as out of each other, or between that object as a whole, and the concomitant conditions under which it is presented to the sense.
Thus, for example, the rays of light in contact with the retina may be perceived either as forming a visible surface, whose parts are related to each other, or as a luminous spot related to the surrounding obscurity: and even a smell or a sound, whether themselves perceived as extended or not, are at all events discerned in and by their relation to different parts of an extended organism.
The sensation and the perception are thus each the necessary condition of the other; and the union of the two is. requisite to constitute a state of consciousness. But consciousness is not complete, even when these two elements are united.
The consciousness of any mental state (whether of sensation or otherwise) never does, and probably never can, take place, without the accompanying consciousness that something else preceded it. This something need not be distinctly known as a former state of consciousness (which would make a beginning of consciousness impossible), just as the space to which the object of perception is related mean that this consciousness is distinct, and can he at that time separated by analysis from its concomitants; but this is equally the case with all the characteristics of sensation.
I only mean that the element of locality is there from the beginning, at least as distinctly as anything else, and that it could be detected if the sensation in its original state could be reproduced in a mind sufficiently developed to be capable of analysing it. In this respect it differs from the acquired perceptions properly so called, such as externality, distance, magnitude, etc., which may be chronologically as well as logically separated from the original sensation.
So long as sensations are spoken of as affections of mind only, there is plausible ground for the opposite opinion; not so, however, when they are viewed in their true character, as affections, neither of mind alone nor of matter alone, but of an animated organism—i.e. of mind and matter together.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the philosophy of consciousness