often a great likeness, though seldom complete accuracy. The belief in the likeness of an image to its prototype is, of course, not generated in this way, but only tested. The belief exists prior to evidence as to its correctness, like most of our beliefs. I shall have more to say on this subject in the next chapter, which will be concerned with memory. But I think enough has been said to show that it is not unreasonable to regard images as having a greater or less degree of resemblance to their prototypes. To claim more is hardly justifiable. We can now reach a definite conclusion about perception, sensation, and images. Let us imagine a number of people placed, as far as possible, in the same environment; we will suppose that they sit successively in a certain chair in a dark room, in full view of illuminated pictures of two eminent politicians of opposite parties whose names are written underneath them. We will suppose that all of them have normal eyesight. Their reactions will be partly similar, partly different. If any of these observers are babies too young to have learnt to focus, they will not see sharp outlines, but a mere blurr, not from an optical defect, but from a lack of cerebral control over muscles. In this respect, experience has an effect even upon what must count as pure sensation. But this difference is really analogous to the difference between having one’s eyes open and having them shut; the difference is in the sense-organ, although it may be due to a difference in the brain. We will therefore assume that all the spectators know how to adjust the eyes so as to see as well as possible, and all try to see. We shall then say that, if the spectators differ as widely as is possible for normal human beings, what is common to the reactions of all of them is sensation, provided it is connected with the sense of sight, or, more correctly, provided it has that quality which we observe to be common and peculiar to visual objects. But probably all of them, if they are over three months old, will have tactile images while they see the pictures. And if they are more than about a year old, they will interpret them as pictures, which represent three-dimensional objects; before that age, they may see them as coloured patterns, not as representations of faces. Most animals, though not all, are incapable of interpreting pictures as representations. But in an adult human being this interpretation is not deliberate; it has become automatic. It is, I think, mainly a question of tactile images: the images you have in looking at a picture are not those appropriate to a smooth flat surface, but those appropriate to the object represented. If the object represented is a large one, there will also be images of movement--walking round the object, or climbing up it, or what not. All these are obviously a product of experience, and therefore do not count as part of the sensation. This influence of experience is still