SENSATION, a name of great import in the philosophy of mind, as well as familiar in ordinary speech. Tn the mental process so named, there is a concurrence of many contrasting phenomena, rendering the word ambiguous, and occasioning verbal disputes.
I. In sensation there is a combination or concurrence of physical facts with a men tal fact, and the name is apt to be employed in expressing either side. Thus, in sight, the physical processes are known to be—the action of light upon the globe and retina of the eye, a series of nerve-currents in the brain, and a certain outgoing influence to mus cles and viscera; these are accompanied by the totally different phenomenon termed the feeling, or the mental consciousness of light. It is to the last fact, the mental fact, that the name sensation is most correctly applied; but there is a natural liability to make it include those physical adjuncts wh-cli arc inseparable from the mental manifestations.
2. In the still more comprehensive contrast of mind and the external or extended world, both members may be designated under sensation. One and the stune situation on our part may contain a strictly mental or subjective experience—pleasure or pain, for example—and an objective experience, or a recognition of the extended world, as distinct from mind. In looking at a fine prospect, both facts concur in fluctuating proportions; we have a feeling of pleasure (mind or subject) and a knowledge of the outspread or extended world (object). which is what affects us in the same way at all times, and affects all minds alike. As before, sensation is most properly used to express the strictly mental or subjective experience, the pleasure or the pain, while the "perception" should be applied to express the objective experience. See PERCEPTION.
3. In sensation, a past experience recovered by memory is inextricably woven with the present impression, a circumstance which confuses the boundary-line between sense and intellect. The sensation that the full moon gives rise to is not solely owing to the
present effect of the moon's rays on the organs of vision; the present effect revives or restores the total ingrained impression of the moon consequent on all the occasions when we have observed it. Again, it is impossible for us to have a sensation without a more or less complex feeling of difference or discrimination, which property is a fundamental fact of intellect. Onr sensation of the 'noon supposes a contrast of the white light with the adjoining blue, of the round form with other forms, of the broad disk with a starry 'point, and so on. Thus, in sensation we have a concurrence of all three processes of the intellect—retentiveness, agreement., and'differenee. Sensation without intellect is a mere abstraction; it is never realized in fact.
This last remark has important bearings upon the question as to the origin of our knowledge. It has been disputed whether or not our ideas are wholly derived from sense. Now, seeing that there is no such thing as sense to the exclusion of intellect, the question ought to be enlarged and put in this form, Are our ideas wholly derived through sense in conjunction with the intellectual processes, or are there any ideas thud are not or Cannot be so derived? When it is alleged by Cudworth, Price, and others, by way of maintaining the doctrine of innate ideas, that likeness, unlikeness, equality, proportion, etc„ are not obtained from sense, the answer is, that their origin may in all probability _be accounted for by sense co-operating with the well-known powers of the intellect, and that, until the conjunction of the two is proved insufficient, the theory of an intuitive origin is not called for.