17. It is, then, necessary to distinguish between the certainty of the human race and philosophical certainty, although, to speak frankly, it is not easy to conceive what can be the value of any human certainty distinct from that of the human race. If we set aside the efforts which the philosopher sometimes makes to discover the basis of human knowledge, we shall readily find him confounded with the rest of mankind. This cavil leaves no trace in his mind with respect to the certainty of all that the human race is certain of. He then discovers that the doubt which he felt was not a real doubt, although he may have deluded himself into a contrary belief. His doubts were simple suppositions, nothing more. When his meditation is over, and perhaps even while it lasts, he finds that he is as certain as the most ignorant individual of his internal acts, the existence of his own body, of other bodies around him, and of a thousand other things, which constitute the amount of knowledge requisite to the wants of life. Question all, from the infant of a few summers, to the sage of many years and mature judgment, on the certainty of their own existence, their acts internal or external, their friends and relatives, the people among whom they dwell, objects seen or heard of, and you will not detect any hesitation in their answers, or any kind of difference in the grades of their certainty. If they have no knowledge of the philosophical questions touching these matters, you may read in their countenances wonder and astonishment that any one should seriously investigate things so _evident_. 18. Impossible as it is for us to know in what manner the sensitive, intellectual, and moral powers of children are developed, it is equally impossible to prove a _a priori_, by analyzing the operations of his mind, that reflex acts do not concur to the formation of certainty; but it will not be difficult to find proofs of this in the exercise of these faculties when well developed. If we observe attentively, we shall see that the child's faculties habitually operate in a direct, not a reflex manner; which shows that the development is made directly, not by reflection. Were the primitive development the work of reflexion, the reflective power would be great in the child. But this is not the case. Very few men are ever endowed with it, and in the greater part of them it is very nearly null. They who attain to it, acquire it only by assiduous labor, and not without great violence to himself, can any one pass from direct to reflex cognition. 19. No matter what you teach a child, he perceives it indeed, but call his attention to the perception itself, and his understanding is at once obscured and confused. Let us make the experiment. Suppose we would teach a child the elements of geometry.