As regards his doctrines of practical reason, which we are here beginning to consider, it might be thought that Vico, unlike his attitude with regard to the theoretical reason, did not stand in sharp opposition to the thought of his time, but actually united himself with a contemporary movement, namely the school of natural rights. The head of the school and leader of the movement, Hugo Grotius, was called by Vico one of his "four authors," together with Plato, from whom he had drawn his aspirations towards an idealistic philosophy, Bacon, who had aroused in his mind the idea of a positive and historical science of society, and Tacitus, his debt to whom, or at least the debt which he believed he owed him, we shall examine later on. Along with Grotius he frequently mentions the other chief authorities on natural rights, Selden and Puffendorf, omitting their innumerable followers, whom he considers less as scientific authorities than as "adorners" of the Grotian system. His adherence to the school, in a certain sense, is clear, and is admitted and proclaimed by Vico himself. But it is also beyond doubt that he was no mere adherent: he was not a follower of the kind that retains the general or leading ideas while developing and correcting details. He was a follower in the dialectical sense only, that is, in so far as he thought it necessary to contest the primary theses, or to accept them only in a profoundly modified form. Natural right offered him not solutions but problems: and of these, while some came before him already clearly formulated, others, and these were the more important, arose only in his own mind: problems either unsolved or unrealised, till Vico propounded and in part solved them.