Reid has faith in the fact - for his common sense assures him of it - that a lasting substantiality lies behind the world of the senses, even if for human consciousness it exists only so long as impressions of it are received via the bodily senses. Similarly, he has faith in the fact that his consciousness, although existing but intermittently, has as its bearer a lasting self. Instead of allowing this intuitively given knowledge to be shaken by a mere staring at fugitive pictures, behind which the real existence of self and world is hidden, he seeks instead in both directions for the origin of the pictures and will not rest until he has found the lasting causes of their transient appearances.
In one direction Reid finds himself led to the outer boundary of the body, where sense perception has its origin. This prompts him to investigate the perceptions of the five known senses: smelling, tasting, hearing, touching and seeing, which he discusses in this order. In the other direction he finds himself led - and here we meet with a special attribute of Reid's whole philosophical outlook - to the realm of human speech. For speech depends upon an inner, intelligent human activity, which, once learnt, becomes a lasting part of man's being, quite outside the realm of his philosophizing consciousness, and yet forming an indispensable instrument for this consciousness.
The simplest human reasoning, prompted only by common sense, and the subtlest philosophical thought, both need language for their expression. Through his ability to speak, man lifts himself above an instinctive animal existence, and yet he develops this ability at an infantile stage, when, in so far as concerns the level of his consciousness and his relationship to the world, he hardly rises above the level of the animal. It requires a highly developed intelligence to probe the intricacies of language, yet complicated tongues were spoken in human history long before man awoke to his own individual intelligence. Just as each man learns to think through speaking, so did humanity as a whole. Thus speech can become a means for acquiring insight into the original form of human intelligence. For in speech the common sense of man, working unconsciously within him, meets the fully awakened philosophical consciousness.3
The way in which the two paths of observation have here been set out must not give rise to the expectation that they are discussed by Reid in a similarly systematic form. For this, Reid lacked the sufficient detachment from his own thoughts. As he presents his observations in the Inquiry they seem to be nothing but a systematic description of the five senses, broken into continually by linguistic considerations of the kind indicated above. So, for example, many of his more important statements about language are found in his chapter on 'Hearing'.
Our task will be to summarize Reid's work, taking from his description, so often full of profound observations, only what is essential to illustrate his decisive discoveries. This requires that (keeping to Mr. Eraser's picture) we consider separately the two pillars supporting the roof of the temple's forecourt: speech and sense-impressions. We will start with speech.
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Reid notes as a fundamental characteristic of human language that it includes two distinct elements: first, the purely acoustic element, represented by the sheer succession of sounds, and secondly the variety of meanings represented by various groups of sounds, meanings which seem to have nothing to do with the sounds as such. This state of language, where the sound-value of the word and its value as a sign to denote a thing signified by it, have little or nothing to do with one another, is certainly not the primeval one. In the contemporary state of language, which Reid calls artificial language, we must see a development from a former condition, which Reid calls natural language. So long as this latter condition obtained, man expressed in the sound itself what he felt impelled to communicate to his fellows. In those days sound was not merely an abstract sign, but a gesture, which moreover was accompanied and supported by the gestures of the limbs.
Even to-day man, at the beginning of his life, still finds himself in that relationship to language which was natural to all men in former times. The little child acquires the ability to speak through the imitation of sounds, becoming aware of them long before it understands the meaning accorded to the various groups of sounds in the artificial state of contemporary adult speech. That the child's attention should be directed solely to the sound, and not to the abstract meaning of the individual words, is indeed the prerequisite of learning to speak. If, says Reid, the child were to understand immediately the conceptual content of the words it hears, it would never learn to speak at all.
When the adult of to-day uses language in its artificial state, words are only signs for things signified by them. As he speaks, his attention is directed exclusively towards this side of language; the pure sound of the words he uses remains outside the scope of his awareness. The little child, on the other hand, has no understanding of the meaning of words and therefore lives completely in the experience of pure sound. In the light of this, Reid comes to the conclusion, so important for what follows, that with the emergence of a certain form of consciousness, in this case that of the intellectual content of words, another form submerges, a form in which the experience of the pure sound of words prevails. The adult, while in one respect ahead of the child, yet in another is inferior, for the effect of this change is a definite impoverishment in soul-experience. Reid puts this as follows:
'It is by natural signs chiefly that we give force and energy to language; and the less language has of them, it is the less expressive and persuasive. ... Artificial signs signify, but they do not express; they speak to the understanding, as algebraic characters may do, but the passions and the affections and the will hear them not: these continue dormant and inactive, till we speak to them in the language of nature, to which they are all attention and obedience.'