(_d_) The third period extends from the twelfth to the fifteenth year. It is the period of intellectual development. With no habits of thought or study, being little else than a robust animal, in three years _Emile_ is to obtain all needed intellectual training. True, Rousseau excludes everything that is not useful, and places limitations even on that. For example, he naturally lays great stress upon the physical sciences which are to be taught in connection with things themselves,--out of doors, by travel, and in actual life; but he allows no history, or grammar, or ancient languages. No books are permitted save "Robinson Crusoe," which Rousseau finds entirely suitable for _Emile_. A trade is to be learned during this period. While in general we condemn Rousseau's scheme of education, there is much in his methods that is most excellent. On this point Compayre comments as follows: "At least in the general method which he commends, Rousseau makes amends for the errors in his plan of study: 'Do not treat the child to discourses which he cannot understand. No descriptions, no eloquence, no figures of speech. Be content to present to him appropriate objects. Let us transform our sensations into ideas. But let us not jump at once from sensible to intellectual objects. Let us always proceed slowly from one sensible notion to another. In general, let us never substitute the sign for the thing, except when it is impossible for us to show the thing.'"[125] (_e_) The fourth period of education begins at fifteen, the period of adolescence. At this time, "_Emile_ will know nothing of history, nothing of humanity, nothing of art and literature, nothing of God; but he will know a manual trade." Rousseau himself says, "_Emile_ has but little knowledge, but that which he has is really his own; he knows nothing by halves." He has a mind which, "if not instructed, is at least capable of being instructed." The remaining work to be done in the education of _Emile_ consists in training the sentiments of affection, the moral and the religious sentiments. The feeling of love for his fellow-beings is now to be cultivated. The error of this is shown by Compayre, who says, "For fifteen years Rousseau leaves the heart of _Emile_ unoccupied.... Rousseau made the mistake of thinking that a child can be taught to love as he is taught to read and write, and that lessons could be given to _Emile_ in feeling just as lessons are given to him in geometry." In morals Rousseau taught that the first duty of every one is to take care of himself; we must love ourselves first of all, and find our greatest interest in those things that best serve us. We must seek that which is useful to us and avoid what harms us, instead of loving our enemies and doing good to those that hate us, as taught by Christ. We must love those who love us, while we must avoid and hate those who hate us.