Images as data--Nerves, afferent and efferent, cannot beget images, nor can the brain give rise to representations--All our perception relative to action. Denial of this involves the fallacies of Idealism or of Realism--Perception and knowledge--Physiological data--Zone of indetermination--"Pure" perception--Memory and Perception. From the study of Change we are led on to a consideration of the problems connected with our perception of the external world, which has its roots in change. These problems have given rise to some very opposing views--the classic warfare between Realism and Idealism. Bergson is of neither school, but holds that they each rest on misconceptions, a wrong emphasis on certain facts. He invites us to follow him closely while he investigates the problems of Perception in his own way. "We will assume for the moment that we know nothing of theories of matter and theories of spirit, nothing of the discussions as to the reality or ideality of the external world. Here I am in the presence of images, in the vaguest sense of the word, images perceived when my senses are opened to them, unperceived when they are closed. ... Now of these images there is ONE which is distinct from all the others, in that I do not know it only from without by perceptions, but from within by affections; it is my body." [Footnote: Matter and Memory, p. 1 (Fr. p. 1).] Further examination shows me that these affections "always interpose themselves between the excitations from without and the movement which I am about to execute." [Footnote: Matter and Memory, p. 1 (Fr. p. 1).] Indeed all seems to take place as if, in this aggregate of images which I call the universe, nothing really new could happen except through the medium of certain particular images, the type of which is furnished me by my body." [Footnote: Matter and Memory, p. 3 (Fr. p. 2).] Reference to physiology shows in the structure of human bodies afferent nerves which transmit a disturbance to nerve centres, and also efferent nerves which conduct from other centres movement to the periphery, thus setting in motion the body in whole or in part. When we make enquiries from the physiologist or the psychologist with regard to the origin of these images and representations, we are sometimes told that, as the centrifugal movements of the nervous system can evoke movement of the body, so the centripetal movements--at least some of them--give rise to the representation, mental picture, or perception of the external world. Yet we must remember that the brain, the nerves, and the disturbance of the nerves are, after all, only images among others. So it is absurd to state that one image, say the brain, begets the others, for "the brain is part of the material world, but the material world is not part of the brain." Eliminate the image which bears the name 'material world,' and you destroy, at the same time, the brain and the cerebral disturbances which are parts of it.