What remains to be done when we have observed all that lies around us? We must turn to our own use all that we can get, we must increase our comfort by means of our curiosity. Hitherto we have provided ourselves with tools of all kinds, not knowing which we require. Perhaps those we do not want will be useful to others, and perhaps we may need theirs. Thus we discover the use of exchange; but for this we must know each other's needs, what tools other people use, what they can offer in exchange. Given ten men, each of them has ten different requirements. To get what he needs for himself each must work at ten different trades; but considering our different talents, one will do better at this trade, another at that. Each of them, fitted for one thing, will work at all, and will be badly served. Let us form these ten men into a society, and let each devote himself to the trade for which he is best adapted, and let him work at it for himself and for the rest. Each will reap the advantage of the others' talents, just as if they were his own; by practice each will perfect his own talent, and thus all the ten, well provided for, will still have something to spare for others. This is the plain foundation of all our institutions. It is not my aim to examine its results here; I have done so in another book (Discours sur l'inegalite). According to this principle, any one who wanted to consider himself as an isolated individual, self-sufficing and independent of others, could only be utterly wretched. He could not even continue to exist, for finding the whole earth appropriated by others while he had only himself, how could he get the means of subsistence? When we leave the state of nature we compel others to do the same; no one can remain in a state of nature in spite of his fellow-creatures, and to try to remain in it when it is no longer practicable, would really be to leave it, for self-preservation is nature's first law. Thus the idea of social relations is gradually developed in the child's mind, before he can really be an active member of human society. Emile sees that to get tools for his own use, other people must have theirs, and that he can get in exchange what he needs and they possess. I easily bring him to feel the need of such exchange and to take advantage of it.