of deviation, but there is only one possibility = the use of former experiences.
But what good can old experiences do in a new situation, which is quite different? (It is true if there were absolutely no resemblance between the old and the new, reason would be staggered and surprised and unable to give any advice: but this never happens except in earliest youth. It is the function of reason to detect similarities between the new and the old, between one object and another. However different two things or events may be: analysis will usually discover that both are composed of similar elements, only in different combinations.)
(Suppose a man were suddenly brought to a foreign country with a climate and plants and animals quite different from his own: he need not perish, as an animal might, but by comparing the new circumstances with the old ones would find means of sustaining and protecting himself, would discern between friend and enemy, useful and harmful plants, and would not be defeated by the cold of winter even he has never experienced it with the same intensity before.)
Reason enables man to find his way about in the world, firstly by preventing him from ever being taken completely by surprise and being baffled: he will know how new things behave because he will recognise them as combinations of known things; and secondly by helping him to make inventions, i. e. intentionally creating new combinations of old elements in order to produce effects which would otherwise be unattainable.
In every case the practical aim of knowledge is prediction, and we have good reasons to regard as the defining characteristics of knowledge those properties of it which make prediction possible. „Savoir pour prévoir." Prediction requires mental anticipation of future events, a survey of possible combinations of given elements. This cannot be accomplished by taking the real elements and arranging them in various orders — that would be trying out, and not predicting: we want to judge about possible combinations before they have actually come into existence. It is necessary, therefore, to replace the real objects by something else that can represent them in the game of combinations, i. e. by symbols which can easily be handled. The role of these signes is played either by so — called mental pictures, which we can arrange and rearrange in our imagination (and this
