principle of non-vigilance. In the 16th century, asked by the Spanish monarchs to investigate the legitimacy of claims to land dominion by the indios of Latin America, Francisco de Vitoria expounded a theory of natural rights, especially in his famous Relectio de Indis. In the 17th century Thomas Hobbes founded a contractualist theory of legal positivism beginning from the principle that man in the state of nature, which is to say without a "commonwealth" (a state) is in a state of constant war one with the other and thus in fear of his life and possessions (there being no property nor right without a sovereign to define it). Hobbes asserted natural law as how a rational human, seeking to survive and prosper, would act; the first principle of natural law being to seek peace, in which is self-preservation. Natural law (which Hobbes accepted was a misnomer, there being no law without a commonwealth) was discovered by considering humankind's natural interests, whereas previous philosophers had said that natural rights were discovered by considering the natural law. In Hobbes' opinion, the only way natural law could prevail was for human beings to agree to create a commonwealth by submitting to the command of a sovereign, whether an individual or an assembly of individuals. In this lay the foundations of the theory of a social contract between the governed and the governor. Hugo Grotius based his philosophy of international law on natural law. He wrote that "even the will of an omnipotent being cannot change or abrogate" natural law, which "would maintain its objective validity even if we should assume the impossible, that there is no God or that he does not care for human affairs." (De iure belli ac pacis, Prolegomeni XI). This is the famous argument etiamsi daremus (non esse Deum), that made natural law no longer dependent on theology. John Locke incorporated natural law into many of his theories and philosophy, especially in Two Treatises of Government. Locke turned Hobbes' prescription around, saying that if the ruler went against natural law and failed to protect "life, liberty, and property," people could justifiably overthrow the existing state and create a new one. The Belgian philosopher of law Frank Van Dun is one among those who are elaborating a secular conception of natural law in the liberal tradition. There are also emerging and secular forms of natural law theory that define human