98 



METAPHYSICS. 



Meiaphy- but sensations, which, in general, we can refer to cer- 

 ! tain organs ; but beyond that every thing is inscrutable ; 



"Y" and we may say of sensation what St. Augustine said 

 of time, Si non rogcx, intelligo. 



There is another circumstance which has misled phi- 

 losophers on this subject. In vision, for instance, an 

 actual picture is painted on the relina, and when this 

 picture is not produced, there is no perception of visible 

 objects. This lends some countenance to the opinion, 

 that an actual picture must be presented to the mind 

 in every act of perception. This is the most favourable 

 example that can be produced in support of the doc- 

 trine of ideas ; and yet we do not see that it advances 

 our knowledge a single step as to the real nature of 

 perception. We have got an additional preliminary 

 fact ; but we can scarcely be said to be nearer to ulti- 

 mate knowledge ; and the optician or phisiologist who 

 is most intimately acquainted with the structure of the 

 eye, knows no more of the nature of perception, than 

 the clown who never heard of its lens, or coats, or hu- 

 mours. 



They who have attempted to combine physiology 

 with metaphysics, have endeavoured to penetrate a little 

 farther behind the scenes, and have carried the image 

 from the relina to the brain by means of the optic 

 nerve. They have, no doubt, some grounds for this 

 process ; for when the optic nerve is destroyed, no sen- 

 sation is produced. But it is quite clear that the 

 image on the retina cannot be transmitted through the 

 nerve on any principle of optics or mechanical philoso- 

 phy. The picture on the retina is exactly the same as 

 that which is produced by means of any lens similarly 

 constructed : and even supposing it carried, by any 

 process, to the brain, we still know no more of per- 

 ception than we did before. For why should the mind 

 be able to perceive this image rather than the object it- 

 self from which it proceeds ? 



But, then, it is argued, that as we know for certain, 

 that external objects cannot be present to the mind ; 

 (because the mind itself perceives that they are at a 

 distance ;) there must be some representations, or ima- 

 ges of them, present to the mind, since a thing cannot 

 act where it is not. Here again the principles of me- 

 chanical philosophy are brought in to explain a subject to 

 which they are entirely inapplicable. It is said, indeed, 

 that our senses are adapted for the communication of cer- 

 tain sensations. Taste, smell, sounds, are confined to par- 

 ticular organs ; and without these organs, we can have 

 no conception that such sensations could be excited : 

 yet these sensations, as well as every other, are mere 

 affections of our minds, bearing no conceivable resem- 

 blance to the qualities in external nature which produce 

 them. Taste, and smell, and sound, are no more like 

 any thing we perceive in the qualities of matter, than 

 the written characters in music are like the melodious 

 tunes which they represent. 



The im- We hold, then, that the affections of the senses are 



pressiotu mere signs, or signals to the mind, to excite certain sus- 

 on the ceptibilities, or to call into exercise certain faculties, 

 rises are rp^; s p er },aps might be admitted by all parties upon al- 

 16 lowing them to fix their own interpretation upon it. 

 The Peripatetics and Cartesians would say, that the 

 signs call the mind to the consideration of the subject, 

 in the same manner as the picture of an acquaintance 

 brings him to our recollection : whilst others would say, 

 that they are arbitrary but invariable signs established 

 by the author of our nature ; bearing no kind of re- 

 semblance to the things which they represent, yet ex- 

 hibiting them to the mind as infallibly, as the arbitrary 

 characters of a known language convey to our minds 



an idea of the sentiments which they represent. The Metaphy- 

 only difference between the two cases is this : that in s 's- 

 the one, the signs are fixed by God, and are immutable ; '*""V~' 

 whilst in the other, they are selected by ourselves, and 

 may be altered or varied at pleasure. 



We venture, then, to call the intimations of our senses 

 natural characters, which the author of our being has 

 established as the indices of certain sensations: and 

 there is, perhaps, about the same connection between 

 the signs and the things signified, as there is between a 

 smile and the feeling of happiness. A smile is not an 

 artificial sign : (at least we dislike it very much when 

 it assumes this character :) we are irresistibly impell- 

 ed, by the constitution of our nature, to express certain 

 feelings by certain modifications of the features. 



Format enim natura prius nos intus ad omncni 



Forti/narttm liaUtum ; juvat, aut impel/it ad Iran, 



Aut ad hiimum mccrore gram dcducit et aug'tt : 



Post ej/'ert uniml motus intcrprcle lingua, 



There is nothing left to accident here: every thing is 

 fixed and determined; and a man generally makes a 

 very awkward figure when he endeavours to exhibit the 

 signs of emotions different from those which he actual- 

 ly feels. Yet, can any possible connection be traced 

 between the feelings of happiness, or grief, or anger, 

 and a particular modification of the muscles of the face ? 

 It is to no purpose that we are told, that certain emo- 

 tions put in action certain muscles about the heart, we 

 shall say ; and that these muscles affect others which, 

 in their turn, communicate the impulse, till the result 

 is depicted in the human countenance. This is, no 

 doubt, a very interesting subject of study to the ana- 

 tomist or physiologist ; but it is perfectly useless to 

 the metaphysician who is inquiring into the origin of 

 sensations, and the connection between natural organs 

 and a thinking spiritual substance. All that the ana- 

 tomist does is to describe the machinery ; the metaphy- 

 sician endeavours to ascertain the principle of motion. 



But, then, some metaphysicians affirm that the per- The per- 

 ception of objects is not immediate ; but that the rapi- c e P tlon p f 



dity with which we interpret the signs is the result of . ject f. 



1 . , r . . ,, . . it . . immediate. 



early and deep-rooted association. This is the opinion 



of Hartley and of many others. Dr. Porterfield says, 

 that " it is not the external sun and moon which are in 

 the heavens, that our mind perceives, but only their 

 image or representation impressed on the sensorium." 

 Perhaps we do not perceive any of the objects of nature 

 as they really are ; yet this does not interfere with our 

 ready and rapid apprehension of them. The picture 

 of objects always>appears inverted on the relina, yet we 

 always perceive them in their right posture. Philoso- 

 phers and physiologists have puzzled themselves ex- 

 ceedingly to account for this ; but all to no purpose. 

 They talk of the rays which proceed from the object, 

 crossing each other in the eye, so that those which come 

 from the upper part of the object strike on the under 

 part of the relina, and vice iiersi ; and therefore they 

 imagine that we perceive objects in their right posture, 

 in the same manner as we would judge an object which 

 strikes the roof of a room to come from below. This is 

 egregious trifling : was any man alive ever sensible of 

 any crossing of the rays, or of any impulse either on the 

 upper or under part of the posteri6r coat of the eye ? 

 The truth is, that in tracing the image to the retina, 

 we are attending only to one stage of the process. We 

 can form no conception whatever of what takes place 

 afterwards; nor can we conceive how it should be easier 

 for the mind to apprehend the image of an object than 

 the object itself. 



It is said, indeed, that there must be a communica- 



