"Do you see this figure bounded by three lines? It is called a triangle; the lines are called sides, and the points where they unite the vertices of the angles."--"I understand that."--"Do you see this other figure bounded by four lines? It is called quadrilateral, and, like the triangle, has its sides and vertices of angles."--"Very well."--"Can a quadrilateral figure be a triangle, or _vice versa_?"--"It cannot."--"Never?"--"Never."--"Why not?"--"One has three, and the other four sides: how then can they be the same thing?"--"Who knows? It may seem so to you, but--"--"See here! This has three, and this four sides; and three and four are not the same thing." Torture his understanding as much as you please, but you cannot drive him from his position: and thus we see that his perception and his reason operate directly, that is, by direct application to the object. Of himself he does not direct his attention to his own internal acts, does not think upon his own thoughts, does not combine reflex ideas, nor seek in them the certainty of his judgment. 20. And here we detect a vital error in the art of thinking as it has hitherto been taught. The young intellect is exercised in reflection, the most difficult part of science, which is as inconsiderate as it would be to commence his physical development by the most painful gymnastic exercises. Man's scientific development should be governed by his natural development, which is direct not reflex. 21. Let us apply this remark to the exercise of the senses. "Do you hear that music?" asks the child.--"What music?"--"Did you not hear it? Are you deaf?"--"It _seems_ to you that you hear it."--"But, sir, I hear it so distinctly! How can it be possible?"--"But how do you know?"--"I hear it." From his _I hear it_ you cannot drive him: he will not hesitate a moment, nor will he appeal to any reflex act in order to avoid your importunities. "_I hear it_: do not you hear it?" He asks nothing more, and all your philosophy cannot equal the _irresistible force_ of sensation which assures him that there is music, and that whoever doubts it is either deaf or in jest. 22. Had the faculties of the child been developed by alternate direct and reflex acts; had he, when acquiring knowledge of things, thought of something besides the things themselves; evidently a continuation of such acts would have left some impression on his mind, and urged to assign the motives of his certainty, he would indicate those very means that he made use of in the gradual development of his faculties; he would abstract the object, retire into himself, think upon his own thought in one way or another, and thus encounter the difficulty. Nothing of this character takes place, which proves that no such reflex acts have been performed, that there have been only perceptions accompanied by internal consciousness and certainty of their existence; but all in a confused, instinctive manner, without any thing like philosophical reflection.