Bergson begins just the other way up. He starts from the idea of a whole field of direct knowledge vastly more extended than the actual facts of which we are normally aware as making up our direct experience. He calls this whole field of knowledge “virtual knowledge.” This field of virtual knowledge contains the whole of the actions and reactions of matter in which our body has its part at any moment, the multitude of stimulations which actually assail the senses but which we normally disregard, together with all the responses by which our bodies adjust themselves to these stimulations, and, in addition, the whole of our past. For Bergson the problem is to explain, not how we increase our direct knowledge, but how we limit it: not how we remember, but how we forget. “Our knowledge,” he says, “far from being built up by a gradual combination of simple elements, is the result of a sharp dissociation. From the infinitely vast field of our virtual knowledge we have selected, to turn into actual knowledge, whatever concerns our action upon things; the rest we have neglected. The brain appears to have been constructed on purpose for this work of selection. It is easy enough to show that this is so in the case of memory. Our past, as we shall show in the next lecture, is necessarily preserved, automatically. It survives in its entirety. But it is to our practical interest to put it aside, or at any rate only to accept just so much of it as can more or less usefully throw light on the present situation and complete it. The brain enables us to make this selection: it materialises the useful memories and keeps those which would be of no use below the threshold of consciousness. The same thing may be said of perception: perception is the servant of action and out of the whole of reality it isolates only what interests us; it shows us not so much the things themselves as what we can make of them. In advance it classifies them, in advance it arranges them; we barely look at the object, it is enough for us to know to what category it belongs.”[3] [3] _La Perception du Changement_, pages 12 and 13. 27 According to Bergson the facts which we actually know directly in the ordinary course are discriminated out of a very much wider field which we must also be said in a sense to know directly though most of it lies outside the clear focus of attention. This whole field of virtual knowledge is regarded as standing to the actual facts to which we usually devote our attention, much as, for instance, the whole situation of stumbling upon something in a dark room stood to the single quality of roughness: in both cases there is a central point in the full focus of attention which we are apt to look upon as the fact directly known, but this central point is really surrounded by a vastly wider context and this too is known in some sense though it is commonly ignored.