§ 2. Extension as Physically Heal. — We may now proceed to consider the movements of exploration concerned in the apprehension of size and configuration from another point of view. They not only contribute to perception of size and figure, as mere modes of extension; they at the same time yield a perception of external reality. The configuration and size perceived by their means is essentially the configuration and size of bodies existing and persisting independently of us and of percipient activity. In following the contours of an object, our movements are not wholly free, but are bound by certain conditions. We must on the one hand keep in contact with the object, continually preserving the experience of resistance. If contact and resistance cease, we are no longer exploring the object. On the other hand we avoid any effort to overcome resistance by main force; when a body is soft or fragile, this would actually prevent us from attaining our ends, for it would alter the configuration we are exploring; and, in any case, it would be futile. We only feel the resistance in order to yield to it; in this way, it is a condition continually determining our subjective activity. So far as this condition operates, the whole experience is determined for us, not by us, and is therefore the presentation of an external reality. The size and configuration perceived are apprehended as existing independently of our action in perceiving them. The cessation of our activity does not involve the cessation of their existence; they are therefore regarded as persisting even when they are no longer actually presented. This it is which gives the experience practical value, value in the manipulation of objects for the attainment of practical ends. It also explains the sharp antithesis between the successive presentation of the parts of a whole, and their spatial coexistence. The succession is a succession of our subjective states; but the successively apprehended parts persist independently of us and our doings. They therefore coexist independently of us and our doings.