Answer: Social contract has several crucial caracteristics: 1) emerge when the religious justification or interpretation of social order is exhausted/in crisis (Europe 17th century), consequently it is of profane or secular character 2) social contract theory is derived (always) from certain concept of human nature (Hobbes, Locke, Rousseau)....for ex. in Hobbes "homo homini lupus" (human nature) requires absolute monarchy, 3) supposes that social institutions or organization of these institutions determine the quality of social order, 4) society is compared to a machine (mechanistic metaphor of society).
Explanation: psychologically speaking, in 17th and 18th century or in 19th century (Marx) there is still no concept of unconscious and unconscious aspect of human nature. When concept of "unconscious" appears, things will change significantly because discovery of unconscious point at irrational aspect of human nature. In contrast to Enlightenment, after Freud there is not so strong convinction about rational basis of human nature/society.
