Nature advances from what is easy to what is more difficult. It is, therefore, wrong to teach the unknown through the medium of that which is equally unknown. Such errors may be avoided if pupils and teachers talk in the same language and explanations are given in the language that the pupil understands; if grammars and dictionaries are adapted in the language and to the understanding of the pupils; if, in the study of a foreign language, the pupils first learn to understand it, then to write it, and lastly to speak it; if in such study the pupils get to know first that which is nearest to their mental vision, then that which lies moderately near, then that which is more remote, and lastly that which is farthest off; and if children be made to exercise first their senses, then their memory, and finally their understanding. Nature does not overburden herself, but is content with a little at a time; therefore the mental energies of the pupils should not be dissipated over a wide range of subject-matter. Nature advances slowly; therefore school sessions should be shortened to four hours; pupils should be forced to memorize as little as possible; school instruction should be graded to the ages and capacities of the children. Nature compels nothing to advance that is not driven forward by its own mature strength; therefore it follows that nothing should be taught to children not demanded by their age, interests, and mental ability. Nature assists her operations in every possible manner; therefore children should not be punished for inability to learn. Rather, instruction should be given through the senses that it may be retained in the memory with less effort. Nothing is produced by nature the practical application of which is not evident; therefore those things only should be taught whose application can be easily demonstrated. Nature is uniform in all her operations; hence the same method of instruction should be adapted to all subjects of study, and the text-books in each subject should, as far as possible, be of the same editions. Comenius observes that there is a very general complaint that few leave school with a thorough education, and that most of the instruction retained in after life is little more than a mere shadow of true knowledge. He considers that the complaint is well corroborated by facts, and attributes the cause to the insignificant and unimportant studies with which the schools occupy themselves. If we would correct this evil, we must go to the school of nature and investigate the methods she adopts to give endurance to the beings which she has created.