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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; 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 hunan
· [See Gravesande, Introductio ad Philosophiam, cap. xvii.]—2d edit.
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 movements ; [the hand of the one pointing invariably to the same hour with that of the other, while the mechanism of each is a whole within itself, independent of the influence of any foreign powers.]—2d edit. By means of the saine hypothesis, he endeavoured to account for the phenomena of Voluntary Motion. [When I will (for example) to move my arm, the motion is not the consequence of volition, but of the mechanism of the body, rendering this effect simultaneous with the corresponding volition. On the other hand, when an impression is made on an organ of sense, the perception which follows is not the PHYSICAL consequence of the impression, but of the mechanism of the mind, which contains within itself the ideas of all things external; being (as Leibnitz expresses it) a living mirror of the universe, prepared to bring forward and to exhibit, in their just order and succession, the images corresponding to all the different impressions which the organs of sense may receive.] – 2d edit.
39. 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
(3.) By means of the nerves, an impression is made on the brain.
40. 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. Physiologists, as well as metaphysicians, have, in this instance, too frequently lost sight of the just rules of philosopohizing, and have proposed many conjectures which afford no
explanation of the phenomena in question, and which have sometimes led to dangerous conclusions.
SECT. III. —OF ATTENTION.
41. It appears, from the acquired perceptions of sight, that a process of thought may be carried on by the mind, without leaving any trace in the memory; and many
that impressions may be made on our organs of sense, and yet be forgotten next moment. In such cases, our want of recollection is ascribed, even in ordinary conversation, to a want of attention; so that it seems to be a principle sufficiently ascertained by common experience, that there is a certain act or exertion of the mind necessary to fix in the memory the thoughts and the perceptions of which we are conscious. This act is one of the simplest of all our intellectual operations, and yet it has been very little noticed by writers on pneumatology.
42. Having established the certainty of the general fact by an induction of particulars, we are entitled, by all the rules of sound philosophizing, to employ it as a principle for the explanation of other phenomena. Many very curious ones, which are commonly referred to other causes, are resolvable into this principle, in a manner equally simple and satisfactory.
SECT. IV.-OF CONCEPTION.
43. The lower animals, as far as we are able to observe, are entirely occupied with their present sensations and perceptions ; but man is possessed of a faculty by which he can represent to himself sensations of which he has been formerly conscious, and external objects which he has formerly perceived. This faculty may be conveniently distinguished by the name of Conception.
44. The objects of some senses are more easily conceived than those of others ; above all, the objects which are perceived by the eye ; [and hence it is, that in recalling the sensations of Hearing, Smelling, Taste, or Feeling, we naturally avail ourselves, as helps to the memory, of the conceptions of the visible objects with which these sensations happen to be associated in our own minds.]—3d edit. The power of conception, however, may, in the case of all our senses, be greatly improved by experience.
45. It is commonly understood that conception is accompanied with no belief of the existence of its objects; but various considerations render this opinion somewhat doubtful.
46. This faculty has obviously a very intimate connexion with the body. The conception of a pungent taste produces a rush of saliva into the mouth. The conception of an instrument of torture applied to any member of the body, produces a shock similar to what would be occasioned by its actual application.
SECT. V.-OF ABSTRACTION.
47. By our perceptive powers we are made acquainted only with what is particular or individual ; but this description comprehends a very small part of the subjects about which our thoughts are employed. In by far the greater number of instances, our reasonings relate to classes or genera of objects or of events.
48. The process of classification supposes a power of attending to some of the qualities, or circumstances of objects and events, and of withdrawing the attention from the rest. This power is called by logicians Abstraction. It may be defined in more general terms, “The faculty by which the mind separates (or analyzes] the combinations which are presented to it, in order to simplify the objects of its consideration.”
49. An appellative, or a generic word, is a name applicable in common to a number of individuals, which agree with each
, other in some particulars, and differ in others. By means of such words, we are enabled to reason concerning classes of objects and classes of events, and to arrive at general conclusions, comprehending under them a multitude of particular truths. The use which is made in algebra of the letters of the alphabet, affords the best illustration of the nature of general