By the time a child can speak well, he has had a great deal of this kind of experience. Consequently our verbal reactions contain a great deal more objectivity than they would if they came at an earlier stage of infancy. The result is that a number of people can view a scene simultaneously, and use exactly the same words about it. The words which we naturally use in describing what we see are those describing features that will also be evident to others in our neighbourhood. We say, “there is a man”, not, “there is a coloured shape whose visual dimensions are such-and-such an angle vertically, and such another horizontally”. The inference is a physiological inference, and only subsequent reflection makes us aware that it has taken place. We can, however, become aware of it through occasional mistakes; a dot on the window-pane may be mistaken for a man in a distant field. In this case, we can discover our error by opening the window, or by moving the head. In general, however, physiological inferences of this sort are correct, since they have resulted from correlations which are very common, and are likely to be present on a given occasion. Consequently our words tend to conceal what is private and peculiar in our impressions, and to make us believe that different people live in a common world to a greater extent than is in fact the case. We have been using the word “objectivity” in the preceding pages, and it is time to consider exactly what we mean by it. Suppose some scene--say in a theatre--is simultaneously seen by a number of people and photographed by a number of cameras. The impression made upon a person or a camera is in some respects like that made upon other persons and cameras, in other respects different. We shall call the elements which are alike “objective” elements in the impression, and those which are peculiar we shall call “subjective”. Thus those features of shapes which are considered in projective geometry will be objective, whereas those considered in metrical geometry (where lengths and angles are measured) cannot be made objective through sight alone, but demand the use of other senses. In the photographs, a man on the stage will be longer if the camera is near the stage than if it is far off, assuming all the cameras to be alike. But if four actors are standing in a row in one photograph, they will be standing in a row in another; this is an “objective” feature of the impression. And the differences in the visual impressions of a number of spectators with normal eyesight are exactly analogous to the differences in the photographs; so also are the likenesses. Thus the “subjectivity” that we are speaking about at present is something belonging to the physical world, not to psychology. It marks the fact that the stimulus, whether to an eye or to a camera, is not exactly the same wherever the eye or the camera may be placed; there are features of the stimulus which are