We have followed Reid so far in his study of language, because it is along this way that he came to form the concepts that were to serve him as a key for his all-important findings in the realm of sense-experience. These are the concepts which bear on the connexion between the sign and the thing signified; the distinction between the artificial and the natural state of language; and the disappearance of certain primeval human capacities for experience, of which Reid says that they are brought by the child into the world, but fade as his intellectual capacities develop.
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As soon as one begins to study Reid's observations in the realm of sense-experience, one meets with a certain difficulty, noticeable earlier but not so strikingly. The source of it is that Reid was obliged to relate the results of his observations only to the five senses known in his day, whereas in fact his observations embrace a far greater field of human sense-perception. Thus a certain disharmony creeps into his descriptions and makes his statements less convincing, especially for someone who does not penetrate to its real cause.
However this may be, it need not concern us here; what matter to us are Reid's actual observations. For these led him to the important distinction between two factors in our act of acquiring knowledge of the outer world, each of which holds an entirely different place in ordinary consciousness. Reid distinguishes them as 'sensation' and 'perception'. It is through the latter that we become aware of the object as such. But we are mistaken if we regard the content of this perception as identical with the sum total of the sensations which are caused in our consciousness by the particular object. For these sensations are qualitatively something quite different, and, although without them no perception of the object is possible, they do not by themselves convey a knowledge of the thing perceived. Only, because our attention is so predominantly engaged by the object under perception, we pay no heed to the content of our sensation.
To take an example, the impressions of roundness, angularity, smoothness, roughness, colour, etc., of a table contain, all told, nothing that could assure us of the existence of the object 'table' as the real content of an external world. How, then, do we receive the conviction of the latter's existence? Reid's answer is, by entering into an immediate intuitive relationship with it. It is true that to establish this relationship we need the stimuli coming from the impressions which our mind receives through the various senses. Yet this must not induce us to confuse the two.
When nature speaks to man through his senses, something occurs exactly analogous to the process when man communicates with man through the spoken word. In both cases the perception, that is, the result of the process of perception, is something quite other than the sum of sensations underlying it. Per-ceiving by means of the senses is none other than a re-ceiving of nature's language; and this language, just like human language, bears two entirely different elements within it. According as one or the other element prevails in man's intercourse with nature, this intercourse will be either 'natural' or 'artificial' - to use the terms by which Reid distinguished the two stages of human speech.
Just as every human being must once have listened only to the pure sound of the spoken word on a wholly sentient level in order to acquire the faculty of speaking, so also, in order to learn nature's language, the soul must once have been totally surrendered to the pure impressions of the senses. And just as with time the spoken word becomes a symbol for that which is signified by it, the consciousness turning to the latter and neglecting the actual sound-content of the word, so also in its intercourse with nature the soul, with its growing interest in the thing signified, turns its attention more and more away from the actual experiences of the senses.
From this it follows that a philosophy which seeks to do justice to man's whole being must not be satisfied with examining the given content of human consciousness, but must strive to observe the actual process to which this content owes its emergence. In practice this means that a philosopher who understands his task aright must strive to reawaken in himself a mode of experience which is naturally given to man in his early childhood. Reid expresses this in the Inquiry in the following way:
'When one is learning a language, he attends to the sounds, but when he is master of it, he attends only to the sense of what he would express. If this is the case, we must become as little children again, if we will be philosophers: we must overcome habits which have been gathering strength ever since we began to think; habits, the usefulness of which atones for the difficulty it creates for the philosopher in discovering the first principles of the human mind.'
'We must become as little children again, if we will be philosophers!' The phrase appears here almost in passing, and Reid never came back to it again. And yet in it is contained the Open Sesame which gives access to the hidden spirit-treasures of the world. In this unawareness of Reid's of the importance of what he thus had found we must see the reason for his incapacity to develop his philosophy beyond its first beginnings. This handicap arose from the fact that in all his thinking he was guided by a picture of the being of man which - as a child of his time, dominated by the contemporary religious outlook - he could never realize distinctly. Yet without a clear conception of this picture no justice can be done to Reid's concept of common sense. Our next task, therefore, must be to evoke this picture as clearly as we can