155. We have given the name of intellectual instinct to the impulse which in many cases produces certainty without the aid of the testimony either of consciousness or of evidence. If you show a man a target, then blindfold his eyes, and turn him around at random several times, and, after this, place a bow in his hands, and assure him that the arrow will strike the precise centre of the target, he will say that this is impossible; and nothing can induce him to believe so great an absurdity. And why not? Because of the testimony of consciousness? No! For the question is now of external objects. Neither does he depend on evidence; for the objects of evidence are things necessary, and it is not intrinsically impossible for the arrow to hit the mark assigned. On what then rests his profound conviction that this is not possible? If we suppose him to know nothing of theories, of probabilities, and combinations, to have no knowledge of this science, and never to have so much as thought of such things, his certainty is just as great as it would be were he able to base it upon some sort of calculation. All the bystanders, whether rude or cultivated, ignorant or learned, need no reflection to be equally certain; all will say, or think, "this is impossible; it cannot happen." We again ask, what is the foundation of so strong a conviction? Not springing from consciousness, or from either mediate or immediate evidence, it manifestly can have no other origin than that internal force which we call intellectual instinct, and which may be called common sense, or anything else, so long as the fact itself is recognized. It is a precious gift, which the Creator has given to us, to make us reasonable even before we reason, and to enable us rightly to govern our conduct when we lack time to examine motives of prudence. 156. This intellectual instinct embraces many objects of different orders; it is the guide and the shield of reason: the guide, because it precedes and shows the way; the shield, because it defends reason from her own cavils, and because sophistry becomes dumb in its presence. 157. The testimony of human authority, equally necessary to the individual and to society, commands our assent, by means of an intellectual instinct. Man believes man, believes society, even before thinking of the motives of his faith; few examine them at all, and yet this faith is universal. We do not here inquire if intellectual instinct sometimes deceives, or why, or in what cases it deceives; at present we only seek to establish its existence; and with regard to the errors to which it leads, we shall simply remark, that in a weak being, such as man, the rule is continually changing, and as it is not possible to find a man good, without any admixture of evil, so is it impossible to find truth without some admixture of error.