In human intelligence, as it is now developed, universal and necessary principles are offered to us under forms in some sort consecrated. The principle of causality, for example, is thus enounced to us:--Every thing that begins to appear necessarily has a cause. Other principles have this same axiomatic form. But have they always had it, and did they spring from the human mind with this logical and scholastic apparel, as Minerva sprang all armed from the head of Jupiter? With what characters did they show themselves at first, before taking those in which they are now clothed, and which can scarcely be their primitive characters? In a word, is it possible to find the origin of universal and necessary principles, and the route which they must have followed in order to arrive at what they are to-day? A new problem, the importance of which it is easy to feel; for, if it can be resolved, what light will be shed upon these principles! On the other hand, what difficulties must be encountered! How can we penetrate to the sources of human knowledge, which are concealed, like those of the Nile? Is it not to be feared that, in plunging into the obscure past, instead of truth, one may encounter an hypothesis; that, attaching himself, then, to this hypothesis, he may transport it from the past to the present, and that, being deceived in regard to the origin of principles, he may be led to misconceive their actual and certain characters, or, at least, to mutilate and enfeeble those which the adopted origin would not easily explain? This danger is so great, this rock is so celebrated in shipwrecks, that before braving it one should know how to take many precautions against the seductions of the spirit of the system. It is even conceived that great philosophers, who were timid in no place, have suppressed the perilous problem. In fact, by undertaking to grapple with this problem at first, Locke and Condillac went far astray,[25] and it must be said, corrupted all philosophy at its source. The empirical school, which lauds the experimental method so much, turns its back upon it, thus to speak, when, instead of commencing by the study of the actual characters of our cognitions, as they are attested to us by consciousness and reflection, it plunges, without light and without guidance, into the pursuit of their origin. Reid[26] and Kant[27] showed themselves much more observing by confining themselves within the limits of the present, through fear of losing themselves in the darkness of the past. Both freely treat of universal and necessary principles in the form which they now have, without asking what was their primitive form. We much prefer this wise circumspection to the adventurous spirit of the empirical school. Nevertheless, when a problem is given out, so long as it is not solved, it troubles and besets the human mind. Philosophy ought not to shun it then, but its duty is to approach it only with extreme prudence and a severe method.