In most of these theories and observations, however, the imitative activity has been noticed only in so far as it contributes to the æsthetic delight which may be derived from sensual impressions. But its importance is by no means so restricted as this; on the contrary, we believe it to be a fundamental condition for the existence of intuition itself. Without all these imperceptible tracing movements with which our body accompanies the adaptation of the eye-muscles to the outlines of external objects, our notions of depth, height, and distance, and so on, would certainly be far less distinct than they are.[107] On the other hand, the habit of executing such movements has, so to say, brought the external world within the sphere of the internal. The world has been measured with man as a standard, and objects have been translated into the language of mental experience. The impressions have hereby gained not only in emotional tone, but also in intellectual comprehensibility.[108] Greater still is the importance of imitation for our intuition of moving objects. And a difficult movement itself is fully understood only when it has been imitated, either internally or in actual outward activity. The idea of a movement, therefore, is generally associated with an arrested impulse to perform it.[109] Closer introspection will show every one to how great a part our knowledge, even of persons, is built up of motor elements. By unconsciously and imperceptibly copying in our own body the external behaviour of a man, we may learn to understand him with benevolent or malevolent sympathy.[110] And it will no doubt be admitted by most readers that the reason why they know their friends and foes better than they know any one else is that they carry the remembrance of them not only in their eyes, but in their whole body. When in idle moments we find the memory of an absent friend surging up in our mind with no apparent reason, we may often note, to our astonishment, that we have just been unconsciously adopting one of his characteristic attitudes, or imitating his peculiar gestures or gait.