'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.' 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. * 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.