The more we know, the more mistakes we make; therefore ignorance is the only way to escape error. Form no judgments and you will never be mistaken. This is the teaching both of nature and reason. We come into direct contact with very few things, and these are very readily perceived; the rest we regard with profound indifference. A savage will not turn his head to watch the working of the finest machinery or all the wonders of electricity. "What does that matter to me?" is the common saying of the ignorant; it is the fittest phrase for the wise. Unluckily this phrase will no longer serve our turn. Everything matters to us, as we are dependent on everything, and our curiosity naturally increases with our needs. This is why I attribute much curiosity to the man of science and none to the savage. The latter needs no help from anybody; the former requires every one, and admirers most of all. You will tell me I am going beyond nature. I think not. She chooses her instruments and orders them, not according to fancy, but necessity. Now a man's needs vary with his circumstances. There is all the difference in the world between a natural man living in a state of nature, and a natural man living in society. Emile is no savage to be banished to the desert, he is a savage who has to live in the town. He must know how to get his living in a town, how to use its inhabitants, and how to live among them, if not of them. In the midst of so many new relations and dependent on them, he must reason whether he wants to or no. Let us therefore teach him to reason correctly. The best way of learning to reason aright is that which tends to simplify our experiences, or to enable us to dispense with them altogether without falling into error. Hence it follows that we must learn to confirm the experiences of each sense by itself, without recourse to any other, though we have been in the habit of verifying the experience of one sense by that of another. Then each of our sensations will become an idea, and this idea will always correspond to the truth. This is the sort of knowledge I have tried to accumulate during this third phase of man's life. This method of procedure demands a patience and circumspection which few teachers possess; without them the scholar will never learn to reason. For example, if you hasten to take the stick out of the water when the child is deceived by its appearance, you may perhaps undeceive him, but what have you taught him? Nothing more than he would soon have learnt for himself. That is not the right thing to do. You have not got to teach him truths so much as to show him how to set about discovering them for himself. To teach him better you must not be in such a hurry to correct his mistakes. Let us take Emile and myself as an illustration.