 In the course of pursuing this task, Vico also develops two central themes of his mature philosophy: the outlines of a philosophical system in contrast to the then dominant philosophy of Descartes already criticized in De nostri temporis studiorum ratione, and his statement of the principle that verum et factum convertuntur, that “the true and the made are...convertible,” or that “the true is precisely what is made” (verum esse ipsum factum). Vico emphasizes that science should be conceived as the “genus or mode by which a thing is made” so that human science in general is a matter of dissecting the “anatomy of nature’s works” (DA, 48), albeit through the “vice” of human beings that they are limited to “abstraction” as opposed to the power of “construction” which is found in God alone (DA, 50–52). Given that “the norm of the truth is to have made it” (DA, 52), Vico reasons, Descartes’ famous first principle that clear and distinct ideas are the source of truth must be rejected: “For the mind does not make itself as it gets to know itself,” Vico observes, “and since it does not make itself, it does not know the genus or mode by which it makes itself” (DA, 52). Thus the truths of morality, natural science, and mathematics do not require “metaphysical justification” as the Cartesians held, but demand an analysis of the causes-the “activity”-through which things are made (DA, 64).