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5. Besides these intellectual faculties, which in some degree are common to the whole species, there are other more complicated powers or capacities, which are gradually formed by particular habits of study or of business. Such are, the Power of Taste; a Genius for Poetry, for Painting, for Music, for Mathematics; with all the various intellectual habits acquired in the different professions of life. To analyze such compounded powers into the more simple and general principles of our nature, forms one of the most interesting subjects of philosophical disquisition.
6. To this branch of our constitution may also be referred those auxiliary faculties and principles, which are essential to our intellectual improvement, or very intimately connected with it; in particular, the faculty of communicating our thoughts by arbitrary signs, and the principle of [sympathetic] imitation.
SECT. I. --CONSCIOUSNESS.
7. This word denotes the immediate knowledge which the mind has of its sensations and thoughts, and, in general, of all its present operations,
8. Of all the present operations of the mind, Consciousn is an inseparable concomitant.
9. The belief with which it is attended has been considered as the most irresistible of any; insomuch that this spe of evidence has never been questioned: and yet it rests on the same foundation with every kind of belief to which we are de termined by the constitution of our nature.
10. We cannot properly be said to be conscious of our own existence; our knowledge of this fact being necessarily posterior, in the order of time, to the consciousness of those sensations by which it is suggested.
11. From Consciousness and Memory we acquire the notion, and are impressed with a conviction, of our own personal identity.
SECT. II.---OF THE POWERS OF EXTERNAL PERCEPTION.
ARTICLE FIRST OF THE LAWS OF PERCEPTION IN THE CASE OF OUR
12. Our external senses are commonly reckoned to be five in number, and the same enumeration has been adopted by the soundest philosophers. An attempt has been made by some writers to resolve all our senses into that of feeling ; but this speculation has plainly proceeded from over-refinement, and has no tendency to illustrate the subject of inquiry.
13. Of our five senses there are two, viz., Touch and Taste, in which there must be an immediate application of the object to the organ. In the other three, the object is perceived at a distance by the intervention of a material medium.
14. In order to form an accurate notion of the means by which we acquire our knowledge of things external, it is necessary to attend to the distinct meanings of the words Sensation and Perception. The former expresses merely that change in the state of the mind which is produced by an impression upon an organ of sense; (of which change we can conceive the mind to be conscious, without any knowledge of external objects ;) the latter expresses the knowledge we obtain, by means of our sensations, of the qualities of matter. An indiscriminate use of these two words has introduced much confusion into philosophical disquisitions.
SMELLING, TASTING, AND HEARING. 15. The qualities perceived by Smelling, Tasting, and Hearing, are known to us only as the causes of certain sensations; and have therefore been contradistinguished by the name of Secondary Qualities, from those of which we learn the nature directly and immediately from the sensations with which they are connected. Of this last kind are Extension and Figure;to which (along with some others) Philosophers have given the title of the Primary Qualities of matter.
16. Abstracting from our other organs of perception, Smelling, Tasting, and Hearing could give us no information concerning external objects.
17. Any one of these senses, however, might suggest to the mind (or furnish the occasions of our forming) the simple ideas or notions of Number, Time, Causation, Existence, Personal Identity, and many others.
18. The sense of Touch is spread over the whole surface of the body ; but the hand is more particularly appropriated to this mode of perception ; in consequence, partly of its anatomical structure, and partly of the greater degree of attention we give to the impressions which are made on it.
19. Some of the qualities perceived by this sense are primary, others secondary.-In all its different perceptions, however, there is one common circumstance; that we are not only made acquainted with the existence of some quality or other, but with the particular part of the body to which the external object is applied. It is probably owing to this, that we refer to Touch a variety of sensations which have little or no resemblance to each other; Heat, Itching, Pain, &c. All of these suggest to us the local situation of their exciting causes; and hence we refer them to the same class. [Another circumstance too conspires with this, that Heat and Cold, in common with the other qualities referred to Touch, are perceived by every part of the body, and not by any particular appropriate organs.] - 1st, 2d, 3d editt.
20. The hand is useful in two respects: 1. For examining the properties of bodies, and the laws of the material world; of which properties and laws, none of our other senses, unassisted by that of Touch, could convey to us any accurate knowledge. 2. For the practice of the mechanical arts.— The advantages we derive from it in these respects are so great, that some philosophers, fond of paradoxical opinions, have ascribed to it entirely our intellectual superiority over the brutes.
21. The importance of this organ to man sufficiently intimates the intentions of nature with respect to his ordinary posture; and affordds a refutation of those theories which attempt to class him with the quadrupeds.
22. The description of the Eye, and of the manner in which the pencils of rays, proceeding from the different points of a visible object, are collected by the refractive powers of the humours, so as to form a picture on the retina, belongs properly to optics; but there are many questions arising from this subject, which are intimately connected with the philosophy of the human mind, and which optical writers have in vain attempted to resolve on the common principles of their science. Such are all the questions that relate to the most simple and general laws of vision. These laws are facts which the optician must assume as the groundwork of his reasoning; not difficulties which he is called on to explain.
23. Among the phenomena of vision, more immediately connected with the philosophy of the human mind, the most important are those which depend on the distinction between the original and the acquired perceptions of sight. Prior to experience, all that we perceive by this sense is superficial extension and figure, with varieties of colour and of illumination. In consequence, however, of a comparison between the perceptions of sight and of touch, the visible appearances of objects, together with the correspondent affections of the eye, become signs of their tangible qualities, and of the distances at which they are placed from the organ.
In some cases our judgment proceeds on a variety of these circumstances combined together; and yet, so rapidly is the intellectual process performed, that the perception seems to be perfectly instantaneous.
24. This distinction between the original and the acquired perception of sight, leads to an explanation of many curious phenomena, which had long puzzled those opticians who confined their attention to the mathematical principles of Dioptrics. But to the student of Moral Philosophy it is interesting, chiefly as it affords a palpable and an acknowledged proof, that the mind may carry on intellectual processes which leave no trace in the memory.
25. Two other celebrated questions concerning vision are intimately connected with the philosophy of the mind, and furnish a favourable opportunity for illustrating the limits which nature has prescribed to our inquiries on the subject of perception. The one relates to our seeing objects erect, by means of inverted images on the retina; the other, to our seeing objects single with two eyes.
26. Some of the qualities perceived by sight are primary, others secondary. Extension and figure belong to the former class; colour and varieties of illumination to the latter.
27. The foregoing article naturally leads the attention to the general accommodation of our animal frame to our intellectual faculties. Under this head the following particulars may furnish matter for useful reflections.
(1.) The local distribution of our organs of sense.
(2.) The adaptation of our perceptive powers to the properties and laws of the material world.
(3.) The relation of the stature and strength of man to the physical arrangements on that planet with which he is connected.
(4.) The versatility of his nature; qualifying him to subsist in every variety of climate.
ARTICLE SECOND.-OF PERCEPTION IN GENERAL.
28. Our notions both of body and of mind are merely relative; that is, we can define the former only by the qualities perceived by our senses, and the latter by the operations of which we are conscious.
29. As the qualities of body bear no resemblance to the operations of mind, we are unavoidably led to consider them as perfectly distinct objects of our knowledge; each of which must be studied in its own peculiar way: the one by attention