Cœnæsthesis, the organic dimly-conscious ‘I,’ rises into the clear consciousness of the ‘Ego,’ by excitations of the second order, reaching the brain from the nerves and muscles, for they are stronger and more distinct than the others, and are interrupted. The brain learns the changes produced in the nervous system by external causes, and the contraction of the muscles. How it has knowledge of the latter is still obscure. It has been recently asserted that the muscular sense has for its seat the nerves of the joints. This is certainly false. We have distinct sensations of the contractions of muscles which put no joint in movement--for example, of the orbicular and constrictor muscles. Then there are the cramps and spasms even of isolated muscular fibres, which likewise do not produce a change of position in the joints. But in any case the perceptions of muscular sense exist, however they are or are not produced. Thus consciousness very soon learns that the muscular movements it perceives are preceded by certain acts accomplished by itself, namely, the elaboration of motor images, and the despatch of impulses to the muscles. It receives knowledge of these movements twice, one after the other--it perceives them, first, directly as its own presentation and act of volition, as a motor image elaborated in the nerve-centres; and immediately afterwards as an impression arising from the muscular nerves as accomplished movement. It acquires the habit of connecting its own acts--those previously elaborated motor images--with the muscular movements, and of regarding the latter a consequence of the former--in short, of thinking causally. If consciousness has adopted the habit of causality, it seeks a cause in all its perceptions, and can no longer imagine a perception without a cause. The cause of muscular perceptions--that is, of movements consciously willed--it finds in itself. The cause of nervous perceptions--that is, the information reported by the nervous system concerning the excitations which it experiences--it does not find in itself. But the latter must have a cause. Where is it? As it is not in consciousness, it must necessarily exist somewhere else; there must then be something else outside consciousness, and so consciousness comes, through the habit of causal thought, to assume the existence of something outside itself, of a ‘not-I,’ of an external world, and to project into it the cause of the excitations which it perceives in the nervous system.