Obliged to learn by his own effort, he employs his own reason, not that of another. Most of our mistakes arise less within ourselves than from others; so that if he is not to be ruled by opinion, he must receive nothing upon authority. Such continual exercise must invigorate the mind as labor and fatigue strengthen the body.
The mind as well as the body can bear only what its strength will allow. When the understanding fully masters a thing before intrusting it to the memory, what it afterward draws therefrom is in reality its own. But if instead we load the memory with matters the understanding has not mastered, we run the risk of never finding there anything that belongs to it.
Emile has little knowledge, but it is really his own; he knows nothing by halves; and the most important fact is that he does not now know things he will one day know; that many things known to other people he never will know; and that there is an infinity of things which neither he nor any one else ever will know. He is prepared for knowledge of every kind; not because he has so much, but because he knows how to acquire it; his mind is open to it, and, as Montaigne says, if not taught, he is at least teachable. I shall be satisfied if he knows how to find out the "wherefore" of everything he knows and the "why" of everything he believes. I repeat that my object is not to give him knowledge, but to teach him how to acquire it at need; to estimate it at its true value, and above all things, to love the truth. By this method we advance slowly, but take no useless steps, and are not obliged to retrace a single one.
Emile understands only the natural and purely physical sciences. He does not even know the name of history, or the meaning of metaphysics and ethics. He knows the essential relations between men and things, but nothing of the moral relations between man and man. He does not readily generalize or conceive of abstractions. He observes the qualities common to certain bodies without reasoning about the qualities themselves. With the aid of geometric figures and algebraic signs, he knows something of extension and quantity. Upon these figures and signs his senses rest their knowledge of the abstractions just named. He makes no attempt to learn the nature of things, but only such of their relations as concern himself. He estimates external things only by their relation to him; but this estimate is exact and positive, and in it fancies and conventionalities have no share. He values most those things that are most useful to him; and never deviating from this standard, is not influenced by general opinion.
Emile is industrious, temperate, patient, steadfast, and full of courage. His imagination, never aroused, does not exaggerate dangers. He feels few discomforts, and can bear pain with fortitude, because he has never learned to contend with fate. He does not yet know exactly what death is, but, accustomed to yield to the law of necessity, he will die when he must, without a groan or a struggle. Nature can do no more at that moment abhorred by all. To live free and to have little to do with human affairs is the best way of learning how to die.
In a word, Emile has every virtue which affects himself. To have the social virtues as well, he only needs to know the relations which make them necessary; and this knowledge his mind is ready to receive. He considers himself independently of others, and is satisfied when others do not think of him at all. He exacts nothing from others, and never thinks of owing anything to them. He is alone in human society, and depends solely upon himself. He has the best right of all to be independent, for he is all that any one can be at his age. He has no errors but such as a human being must have; no vices but those from which no one can warrant himself exempt. He has a sound constitution, active limbs, a fair and unprejudiced mind, a heart free and without passions. Self-love, the first and most natural of all, has scarcely manifested itself at all. Without disturbing any one's peace of mind he has led a happy, contented life, as free as nature will allow. Do you think a youth who has thus attained his fifteenth year has lost the years that have gone before?
 This might be carried too far, and is to be admitted with some reservations. Ignorance is never alone; its companions are always error and presumption. No one is so certain that he knows, as he who knows nothing; and prejudice of all kinds is the form in which our ignorance is clothed.
 The armillary sphere is a group of pasteboard or copper circles, to illustrate the orbits of the planets, and their position in relation to the earth, which is represented by a small wooden ball.
 The imaginary circles traced on the celestial sphere, and figured in the armillary sphere by metallic circles, are called culures.
 Rousseau here informs his readers that even these reproaches are expected, he having dictated them beforehand to the mountebank; all this scene has been arranged to deceive the child. What a refinement of artifice in this passionate lover of the natural!