By comparing these two societies, Diderot is able to produce moral statements about the way that people live. The issue of morality is one of Diderot's major themes. From morality Diderot moves to other themes of ownership and private property, specifically through marriage. Both societies seem extremely foreign to one another and think that each are better, but in reality they are just different. Because of his study of nature and the advancements in life sciences, Denis Diderot came to the conclusion that universal progress depends largely on Eros. For Diderot, Eros is "a priori existence of sexual energy that fuels the universe." This concept greatly influenced Diderot's views on human sexuality. His involvement in Enlightenment movements such as sensualism, vitalism and materialism also helped him developed his ideas about human sexuality. He believed that nature had a moral end and encourages humans to have children. Since nature favors procreation, laws and rules should not restrain the sexuality of men and women. Since 18th century French society had many rules controlling people's sexuality, Diderot believed that French society is not a suitable place for Eros because of its "artificiality and formalism." For Claudia Moscovici, Diderot's critique of 18th century French society, especially its rules controlling human sexuality, can especially be seen in the "Supplément au Voyage de Bougainville". Diderot's views on sexuality is contained in the "Supplément au Voyage de Bougainville". In the book, Diderot uses a dialogue between Orou, a Tahitian man, and a chaplain in order to contrast the French and Tahitian societies. Tahitian people are governed by nature and portrayed as happy and content. They also have less restrictions on their sexual conduct because men and women are not obligated to marry before having a child together. People can have sex with the opposite gender in order to procreate, which is nature's intended purpose for humans. In Tahiti, women are not considered property of any man and are not ridiculed for having a child before marriage. Claudia Moscovici argues that Diderot uses the Tahitian society to criticize the laws and norms regarding sexual behavior in 18th century French society and Western culture. Unlike the Tahitians, the French are governed by laws and convention. They had more restrictions on the sexual behavior of men and women. For instance, it was unacceptable to have a child with someone without being married in French society.