To pursue every curiosity and to allow no limits to the thirst for knowledge apart from that of impotence – such zealousness does not ill-become learning. But, from among the innumerable tasks which spontaneously offer themselves, to choose that task, the solution of which is of importance to man – such choice is the merit of wisdom. When science has run its course, it naturally arrives at the point of modest mistrust and says, dissatisfied with itself: How many are the things which I do not understand! But reason, matured by experience into wisdom, serenely speaks through the mouth of Socrates, who, surrounded by the wares of a market-fair, remarked: How many are the things of which I have no need. In this way, two very dissimilar aspirations eventually flow together, even though to begin with they started out in very different directions, the one being vain and dissatisfied, the other composed and contented. For, in order to choose rationally one must already have knowledge of what is superfluous, indeed, impossible. But, eventually science arrives at the determination of the limits imposed upon it by the nature of human reason. All the fathomless projects, however, which may not in themselves, perhaps, be unworthy, except that they lie outside the sphere of man, fly to the limbo of vanity. It is then that even metaphysics becomes that which it is far from being at the moment, and which one would least expect it to be, namely, the companion of wisdom. For, as long as the opinion survives that it is possible to attain to an understanding of such remote things, wise simplicity will call in vain that such great aspirations are superfluous. The feeling of satisfaction which accompanies the extension of knowledge will very easily assume the appearance of dutifulness and convert that deliberate and reflective contentment into the foolish simplicity, which wishes to oppose the ennoblement of our nature.