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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 imitation.

SECTION 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, Consciousness is an inseparable concomitant.

9. The belief with which it is attended has been considered as the most irresistible of any; insomuch that this species of evidence has never been questioned: and yet it rests on the same foundation with every other kind of belief to which we are determined by the constitution of our nature.

10. We cannot properly be said to be conscious of our own existence. It is suggested to us by those sensations and operations of which we are conscious.

11. From Consciousness and Memory we acquire the notion, and are impressed with a conviction, of our own personal identity.

SECTION II.

Of the Powers of External Perception..

ARTICLE FIRST.

Of Perception in general.

12. 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.

13. 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 to the subjects of our Consciousness; the other by attention to the objects of our Perceptions. This is not a hypothesis, but a fact, which is implied in the only notions of body and of mind that we are capable of forming.

14. It appears, however, from the phenomena of perception, and also from those of voluntary motion, that the connexion between body and mind is extremely intimate; and various theories have been proposed, to explain the manner in which it is carried on. All these theories relate to a subject placed beyond the reach of our faculties; and concerning which it is impossible for us to ascertain any thing, but the laws by which the connexion is regulated.

15. In order to form an accurate notion of the Laws of Perception, 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 word Perception expresses the knowledge we obtain, by means of our sensations, of the qualities of matter.

16. It is necessary also to attend to the distinction between Primary and Secondary qualities. The former, although perceived in consequence of certain sensations excited in our minds, are always apprehended as external and independent existences; and the notions of them we form have in general no reference to the sensations by which they are suggested. The truth seems to be, that these sensations were intended by nature to perform merely the office of signs, without attracting any notice to themselves; and, as they are seldom accompanied either with pleasure or pain, we acquire an habitual inattention to them in early infancy, which is not easily to be surmounted in our maturer years. The best examples of this class of qualities are tangible Ex

tension and Figure. Hardness and Softness are commonly referred to the same class; but the propriety of this arrangement may be doubted.

17. Our notions of secondary qualities are merely relative; the sensations which correspond to them informing us of nothing, but of the existence of certain unknown causes by which they are produced. What we know of the nature of these causes is the result of subsequent philosophical investigation. Smell, Sound, Taste, Color, are instances of this class of qualities. The names of secondary qualities are in all languages ambiguous; the same word expressing the sensation, and the unknown cause by which it is excited. Hence may be derived an explanation of the Cartesian paradox, with respect to the non-existence of heat, cold, smell, sound, &c.

18. As our sensations have no resemblance to the qualities of matter, it has puzzled philosophers to explain in what manner our notions of primary qualities are acquired. It is this difficulty that has given rise to the modern scepticism concerning the non-existence of

matter.

19. According to the ancient theory of perception, sensible qualities are perceived by means of images or species propagated from external objects to the mind, by the organs of sense. These images (which since the time of Descartes have been commonly called Ideas) were supposed to be resemblances of the sensible qualities; and, like the impression of a seal on wax, to transmit their form without their matter. This hypothesis is now commonly distinguished by the title of the Ideal Theory.

20. On the principles of this theory, Berkeley demonstrated that the existence of matter is impossible: for, if we have no knowledge of any thing which does not resemble our ideas or sensations, it follows that we have no knowledge of any thing whose existence is independent of our perceptions.

21. If the Ideal Theory be admitted, the foregoing argument, against the existence of matter, is conclusive; but the theory is unsupported by evidence, and is even

inconceivable. That we have notions of external qualities perfectly unlike to our sensations, or to any thing of which we are immediately conscious, is a fact; nor ought we to dispute the reality of what we perceive, because we cannot reconcile this fact with our received philosophical systems.

22. Dr. Reid, who first called the Ideal Theory in question, offers no argument to prove that the material world exists; but considers our belief of it as an ultimate fact in our nature. It rests on the same foundation with our belief of the reality of our sensations, which no man has disputed.

23. Beside the Ideal Theory, other attempts have been made to explain in what manner the communication between mind and matter is carried on, in the case of perception. Leibnitz's system of pre-established Harmony, taking for granted the impossibility of any immediate connexion between two substances essentially different, represents the human mind and human body as two independent machines, adjusted, at their first formation, to an invariable correspondence with each other, like two clocks made to correspond in all their In this manner, he conceived the phenomena of perception, and also those of voluntary motion, to be produced.

movements.

24. The following are the most important general laws of our perceptions, as far as we can infer them from acknowledged facts.

(1.) The object, either immediately, or by means of some material medium, must make an impression on the organ.

(2.) By means of the organ, an impression is made on the nerves.

(3.) By means of the nerves, an impression is made on the brain.

25. With respect, however, to the manner in which this process is carried on, and even with respect to the nature of the changes that take place in the nerves and brain, in the case of perception, we are hitherto ignorant; nor does there seem to be any probability that we shall ever obtain satisfactory information. Physiolo

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gists, as well as metaphysicians, have, in this instance, too frequently lost sight of the just rules of philosophizing, and have proposed many conjectures which afford no explanation of the phenomena in question, and which have sometimes led to dangerous conclusions.

SECTION II.

Of the Powers of External Perception.

ARTICLE SECOND.

Of the Laws of Perception in the case of our different Senses.

26. 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.

27. 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.

28. The qualities perceived by Smelling, Tasting, and Hearing, are secondary; that is, they are known to us only as the causes of certain sensations. Abstracting, therefore, from our other organs of perception, these senses could give us no information concerning external objects.

29. 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.

30. 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.

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