By the beginning of the seventeenth century the idea of a moral law of nature already had a long and complex history. Its ultimate origins go back to the Greek Stoics, for whom the good life was one lived in accordance with nature. In Francis Bacon's writings several conceptions of the law or laws of nature may be distinguished. In some places he referred to one single summary or positive law of nature, whereas in others he referred to 'laws' in the plural. It was in the Principia Philosophiae that Rene Descartes first made public the physical theory of Le Monde, in which he mentioned the three laws of nature. One of the first Descartes's critics was Christiaan Huygens, who in 1652, had come to the conclusion that most of Descartes's collision rules were false. Issac Newton paid relatively little attention to the theory of collisions because he was preoccupied with bodies moving with continuously changing velocities along curvilinear paths.