If we see any object, no matter what, at a proper distance and in sufficient light, we judge of its size, figure, and color, and we are very confident of the truth of our judgment, although we may never, in all our life, have thought of a theory of sensation, or of the relations of our organs, either to each other or to external objects. No reflex act accompanies the formation of our judgment; all is done instinctively, and without the intervention of philosophical considerations. We see it, and nothing else: this is enough for certainty. It is only after having handled books in which the question of certainty is agitated, that we turn our attention to our own acts; but this attention, it is to be remarked, lasts only so long as we are engaged in the scientific analysis; when this is forgotten, which it very soon is, we return to our general routine, and seldom recur to philosophy. Note well that we speak here of the certainty of the judgment formed in consequence of sensation only in so far as it is connected with the uses of life, and not at all of its greater or less exactness with respect to the nature of things. Thus it matters little that we consider colors as inherent qualities of bodies, although in reality they are not; it is sufficient that the judgment formed does not in any sense change our relations to objects, whatever may be the philosophical theory. 27. Example of common sense. In the presence of a numerous assembly, throw a quantity of printer's types at random upon the ground, and tell the bystanders that their names will all be found printed. They will all with one accord laugh at your folly. But what is the reason of this? Have they all reflected upon the basis of their certainty? Assuredly they have not. 28. Example of reason. We all reason, and in many cases rightly. Without art or reflection of any kind, we often distinguish the solid from the futile, the sophistical from the conclusive. This does not require us to regard the course of our understanding; without scarcely noticing it we follow the right road; and a man may, in his life, have formed a thousand rigorous and exact ratiocinations without ever having once attended to his method of reasoning. Even those most versed in the dialectic art, repeatedly forget it; they perhaps follow it very correctly in practice, but they pay no express attention to any one of its rules.