but wanders about upon their surfaces by the help of the senses, examining measurements, actions, resemblances and doctrines. But the knowledge of the mind, which creates the fact, is in a sense itself the fact, just as even among human sciences the knowledge of a triangle, that it has three angles equal to two right angles, is practically identical with the truth itself (_scientia vero mentis, quae res facit, est quasi ipsa res, veluti etiam in humanis scientia trigoni, quod habeat tres angulos duobus rectis aequales, eadem ferme est ipsi veritati_), whence it is clear that there is in us a natural science of a different kind from true science."[29] Here, in the definition of divine knowledge and of the procedure of human knowledge in the case of mathematics, as opposed to that of physical science, is implicit the principle that true knowledge consists in the identity of thought with its object. The idea of the opposition of mathematics to physical science, in the certainty of the one and the uncertainty of the other, persisted in the Neapolitan philosophers and scientists of Vico's youth, even if they lost sight of the reason of this opposition. Tommaso Cornelio in his "progymnasma" _De ratione philosophandi_ (1661) after reviewing the errors produced by the illusions of sense in physical science, says, "the contemplations of mathematics are not subjected to errors of this kind, dealing as they do with things whose images are not introduced into the mind by the senses; for the mind can by itself adequately conceive figures and numbers, whose properties and analogies are examined by mathematicians, without aid from sense."[30] This ought to be emphasised, since it seems highly probable that Vico was stimulated to the establishment of his general theory of knowledge by reflection upon mathematics and the contrast between it and physical science. In fact the Latin speeches, our earliest documents for his studies, though they show the influence of Ficino and a certain amount of Cartesianism,[31] are never dominated by this general criterion. It is only in the last of these speeches, that of 1707, that the distinction between mathematics and natural science begins to appear; in the next year it is clearly stated in the _De ratione studiorum,_ where it takes the form of a general criterion. "We demonstrate geometry because we make it: if we could demonstrate physical facts, we should be creating them. For the true forms of things exist only in God the greatest and best, and to these the nature of them conforms" (_geometrica demonstramus quia facimus: si physica demonstrare possemus, faceremus. In uno enim Deo Opt. Max. sunt verae rerum formae, quibus earundem est conformata natura_). And this theory attained its full development in 1710 in the _De antiquissima._