Sensation, in its most general acceptation, is sometimes used to signify the whole of that portion of considerable misunderstanding. Etymologically, the term should denote a turning lack of the mind upon an object previously existing, so that the existence of a state of consciousness is distinct from the reflection on that state.
In this sense, a sensation, like any other mode of consciousness, may be an object of reflection; and those philosophers who understood Locke in this sense were only consistent in reducing his two sources of ideas to the single one of sensation alone. But, in the greater part of Locke’s Essay, reflection is treated of in a different sense, namely, as the immediate consciousness of our internal states of mind—a consciousness identical with the existence of those states, and thus forming an original source of ideas. Sensation proper is the consciousness of certain affections of our body as an animated organism.
Perception proper is the consciousness of the existence of our body as a material organism, and therefore as extended. The sensitive organism may be considered in two points of view: 1. As belonging to the ego, or conscious subject, which, in its actual concrete existence, is susceptible of consciousness only in and by its relation to a bodily organism. 2. As belonging to the non ego, or material object of consciousness, from which the mind, as an abstract immaterial being, is logically separable; though, in actual consciousness, the two are always united. The bodily organism is thus the debatable land between self and not-self.
In one sense, my eye is a part of my conscious self; for sight is an act of consciousness, and sight cannot exist except by means of the eye. In another sense, my eye is not a part of myself; for a man whose eyes are put out continues to be the same person as before. Hence the organism, as the vehicle of sensation, exhibits in the same act attributes of mind and attributes of body. In the former point of view, the act of sensitive consciousness is regarded as a sensation; in the latter, as a perception.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the philosophy of consciousness