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. *