Fine knowledge, says Vico, this of the clear and distinct idea! That I think what I think is certainly an indubitable fact; but it has by no means the appearance of a scientific statement. Any idea, however false, may seem self-evident: that I think it so does not give it the force of knowledge. That "he who thinks, exists" was a fact well known to Plautus's Sosia, who expressed this conviction in almost the identical words of the Cartesian philosophy: "but when I think, I certainly exist" (_sed quom cogito, equidem certo sum_). But the sceptic will always reply to a Sosia or a Descartes that he has no doubt as to thought; he will even strongly maintain that whatever seems to him cogent is certain, and will uphold it against all objections; and that he has no doubt as to existence: in fact, he is seeking after it in the right way by suspending judgment and not adding to the obscurity of facts other obscurities arising from opinions. But while asserting all this he will still maintain that the certitude of his thought and of his existence is the certitude not of science but of consciousness, and of common consciousness at that. Clear and distinct perception is so far from being science that since, owing to Cartesianism, the principle has been applied to physics, our knowledge of nature has become no more certain. Descartes tried to leap from the plane of common consciousness to that of science: he fell back into common consciousness again without having touched his scientific ideal. But in what does scientific truth consist, if not in immediate consciousness? How does science differ from simple consciousness? What is the criterion, or, in other words, what is the condition which makes science possible? Clearness and distinctness do not take us a step forward. The formulation of an elementary truth does not solve the problem. The question concerns not a primary truth, but the form which truth must have to enable us to recognise it for scientific or real truth. In meeting this question, Vico justified his criticism of the inadequacy of the Cartesian criterion by appealing to a principle which at first sight may seem trite and obvious. It is trite not because of the historic theory with which Vico associated it, a theory later refuted by himself: not, that is, because it belongs to one of the earliest strata of Italian philosophy; but in the sense that it was common to and practically inseparable from Christian thought. To a Christian who declares every day his belief in a God Almighty, Omniscient, Maker of heaven and earth, nothing is more familiar than the assertion that God alone can fully know all things, because he alone is their creator. The primal truth, Vico repeats, is in God, because God is the primal creator. It is an infinite truth because he is the maker of all things, and absolute because it displays to him the internal and external qualities of things, all of which he contains in himself.