The orderliness of nature. Philosophers of the Enlightenment believed that nature is vast and complex but well ordered. The English poet Alexander Pope described nature as "a mighty maze, but not without plan." The philosophers of the period felt that everything in the universe behaves according to a few simple laws, which can be explained mathematically. Their favorite example of such a law was Newton's law of gravity.
Human nature, the philosophers believed, is as well ordered as the physical universe. In The Spirit of the Laws (1748), the French philosopher Montesquieu wrote: "The material world has its laws, the intelligences superior to man have their laws, the beasts their laws, and man his laws." Montesquieu thought that a science of human nature was possible, and he became one of the first philosophers to try to formulate the basic uniformities of all human behavior.
Montesquieu believed that climate has an important influence on temperament and thus on conduct. According to Montesquieu, different kinds of government are appropriate for peoples who are living in different parts of the world. The best government for each nation could be planned, he felt, by considering the country's climate. Montesquieu thought, for example, that free governments are possible in northern latitudes. "People are more vigorous in cold climates," he wrote, and they have a "greater share of frankness and sincerity." But, Montesquieu said, the only workable form of government in a hot climate is despotism (rule by a dictator). Although his conclusions were discarded as mere speculation, they are typical of the Enlightenment's faith in reason.
Literature in the Enlightenment questioned accepted thinking. Writers portrayed human life as changeable and human understanding as partial. Much of the literature was written with self-consciousness and irony. It called attention to conventions and provoked skeptical awareness. The period reached its peak with works such as Pierre de Laclos' Dangerous Liaisons (1782) and the Marquis de Sade's Philosophy in the Bedroom (1795). In these novels, rational thought goes as far as possible toward separating the thinking individual from conventional influences and limitations.
Deism. The philosophers of the Enlightenment were convinced that the universe can be understood by the human mind. This is not an accident, the philosophers emphasized, because God could have created a universe too complex to be grasped by human beings. Instead, God created a universe ideally adjusted to the reasoning powers of people.
Most of the philosophers believed that after God had created the universe, He left it strictly alone. This theory, called deism, rules out the possibility of miracles or other special acts by God. According to deism, God regulated nature so that it proceeds mechanically. Future events are therefore fully predictable on the basis of earlier events. The philosophers liked to think of the universe as a clock that keeps perfect time because it was designed by a superior clockmaker. See Deism.