Establishment of fact is not the simple reception of the faithful imprint of that fact; it is invariably interpreted, systematised, and placed in pre-existing forms which constitute veritable theoretical frames. That is why the child has to learn to perceive. There is an education of the senses which he acquires by long training. One day, which aid of habit, he will almost cease to see things: a few lines, a few glimpses, a few simple signs noted in a brief passing glance, will enable him to recognise them; and he will hardly retain any more of reality than its schemes and symbols. "Perception," says Mr Bergson on this subject, "becomes in the end only an opportunity of recollection." ("Matter and Memory", page 59.) All concrete perception, it is true, is directed less upon the present than the past. The part of pure perception in it is small, and immediately covered and almost buried by the contribution of memory. This infinitesimal part acts as a bait. It is a summons to recollection, challenging us to extract from our previous experience, and construct with our acquired wealth a system of images which permits us to read the experience of the moment. With our scheme of interpretation thus constituted we encounter the few fugitive traits which we have actually perceived. If the theory we have elaborated adapts itself, and succeeds in accounting for, connecting, and making sense of these traits, we shall finally have a perception properly so called. Perception then, in the usual sense of the word, is the resolution of a problem, the verification of a theory. Thus are explained "errors of the senses," which are in reality errors of interpretation. Thus too, and in the same manner, we have the explanation of dreams. Let us take a simple example. When you read a book, do you spell each syllable, one by one, to group the syllables afterwards into words, and the words into phrases, thus travelling from print to meaning? Not at all: you grasp a few letters accurately, a few downstrokes in their graphical outline; then you guess the remainder, travelling in the reverse direction, from a probable meaning to the print which you are interpreting. This is what causes mistakes in reading, and the well-known difficulty in seeing printing errors. This observation is confirmed by curious experiments. Write some everyday phrase or other on a blackboard; let there be a few intentional mistakes here and there, a letter or two altered, or left out. Place the words in a dark room in front of a person who, of course, does not know what has been written. Then turn on the light without allowing the observer sufficient time to spell the writing. In spite of this, he will in most cases read the entire phrase, without hesitation or difficulty. He has restored what was missing, or corrected what was at fault. Now, ask him what letters he is certain he saw, and you will find he will tell you an omitted or altered letter as well as a letter actually written.