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In the Principia (1687), Isaac Newton gave an account of mechanics formulated in terms of precise equations of motion. Given the initial conditions of a system, it was possible to predict completely its future behavior and to retrodict its past. Newton himself did not take a purely mechanical view of the world. There was the mysterious force of gravity, concerning whose origin and nature he declined to frame a hypothesis, and he also believed that the maintenance of the stability of the solar system would require occasional angelic intervention. Newton's eighteenth-century successors, however, had different opinions, and they celebrated the triumph of mechanical thinking. Julien de La Mettrie (1709–1751) wrote his book Man the Machine (1748), and Pierre-Simon de Laplace (1749–1827), in his great work on celestial mechanics, believed that he had established the natural stability of the solar system, so that appeal to the hypothesis of divine assistance in its preservation was no longer necessary.
