We know then, or we may know, the point of departure from which we each start towards the usual level of understanding; but who knows the other extreme? Each progresses more or less according to his genius, his taste, his needs, his talents, his zeal, and his opportunities for using them. No philosopher, so far as I know, has dared to say to man, "Thus far shalt thou go and no further." We know not what nature allows us to be, none of us has measured the possible difference between man and man. Is there a mind so dead that this thought has never kindled it, that has never said in his pride, "How much have I already done, how much more may I achieve? Why should I lag behind my fellows?" As I said before, man's education begins at birth; before he can speak or understand he is learning. Experience precedes instruction; when he recognises his nurse he has learnt much. The knowledge of the most ignorant man would surprise us if we had followed his course from birth to the present time. If all human knowledge were divided into two parts, one common to all, the other peculiar to the learned, the latter would seem very small compared with the former. But we scarcely heed this general experience, because it is acquired before the age of reason. Moreover, knowledge only attracts attention by its rarity, as in algebraic equations common factors count for nothing. Even animals learn much. They have senses and must learn to use them; they have needs, they must learn to satisfy them; they must learn to eat, walk, or fly. Quadrupeds which can stand on their feet from the first cannot walk for all that; from their first attempts it is clear that they lack confidence. Canaries who escape from their cage are unable to fly, having never used their wings. Living and feeling creatures are always learning. If plants could walk they would need senses and knowledge, else their species would die out. The child's first mental experiences are purely affective, he is only aware of pleasure and pain; it takes him a long time to acquire the definite sensations which show him things outside himself, but before these things present and withdraw themselves, so to speak, from his sight, taking size and shape for him, the recurrence of emotional experiences is beginning to subject the child to the rule of habit. You see his eyes constantly follow the light, and if the light comes from the side the eyes turn towards it, so that one must be careful to turn his head towards the light lest he should squint. He must also be accustomed from the first to the dark, or he will cry if he misses the light. Food and sleep, too, exactly measured, become necessary at regular intervals, and soon desire is no longer the effect of need, but of habit, or rather habit adds a fresh need to those of nature. You must be on your guard against this.