ing, 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.

TOUCH.

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 affords a refutation of those theories which attempt to class him with the quadrupeds.

SIGHT.

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 instan

taneous.

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.

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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.

30. 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 anything, but the laws by which the connexion is regulated.

31. According to the distinction formerly stated between the primary and the secondary qualities of matter (15.), our notions of the latter 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. 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 the origin of the Cartesian paradox with respect to the non-existence of heat, cold, smell, sound, and colour.

32. The primary qualities of matter, (such, for example, as Extension and Figure,) 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.

33. As our sensations have no resemblance to the qualities of matter, it has puzzled philosophers to explain in what man

ner 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.

34. 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.

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

36. 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 anything 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.

37. 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.

38. 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 1 [See Gravesande, Introductio ad Philosophiam, cap. xvii.]—2d edit.