A method should be found by means of which each person will be able not only to bring into his mental consciousness that which he has learned, but at the same time to pass sound judgment on the objective facts to which his information refers. This will be possible if only those subjects are studied which will be of real service in the later life; if such subjects be taught without digression or interruption; if a thorough grounding precede the detailed instruction; if all that comes later be based upon what has gone before; if great stress be laid on the points of resemblance between cognate subjects; if the studies be arranged with reference to the pupils’ present mental development, and if knowledge be fixed in the memory by constant use. In support of his principle of thoroughness, Comenius adduces the following proofs from nature: Nothing is produced by nature that is useless. When she forms a body, she omits nothing that is necessary. She does not operate on anything unless it possesses foundations, and she strikes her roots deep and develops everything from them. She never remains at rest, but advances continually; never begins anything fresh at the expense of work already begun, but proceeds with what she has started and brings it to completion. She knits everything together in continuous combination, preserving due proportion with respect to both quality and quantity. Through constant exercise she becomes strong and fruitful. Progress is less a question of strength than of skill. Hitherto little has been accomplished in the school-life of the child, because no set landmarks have been set up as goals to be reached by the pupils; things naturally associated are not taught together; the arts and sciences are scarcely ever thought of as an encyclopædic whole; the methods employed are as numerous and diverse as the schools and teachers; instruction is individual and private, and not public and general, and books are selected with too little regard for the value of their contents. If these matters could be reformed, there is no doubt in the mind of Comenius that the whole circle of the sciences might be covered during the period of school training. Toward the solution of this problem he answers the following questions:—