How do Rousseau and Hobbes' understandings of human nature affect their views of social organization?
Hobbes and Rousseau held very different views of human nature. Hobbes argued that people were essentially equal in basic faculties, but rather than facilitating harmony and peace, this fact actually led to turmoil. Hobbes thought that people were essentially jealous, suspicious, and grasping, and because of this, life in the "state of nature", i.e. before civil society, would be "solitary, poor, nasty, brutish, and short." Out of a strong urge for self-preservation, then, people entered into civil society and established governments. Because Hobbes held such a dim (or, some might say, realistic) view of human nature, he thought that for a government to achieve its purpose, which was to maintain security and safety among men, that government had to be absolutely sovereign. Once men agreed to create government, they surrendered what most would associate with political rights to it.
Rousseau thought that people were inherently good, and that the "natural state of man" was not "solitary, poor, nasty, brutish, and short," but rather peaceful. Directly engaging with Hobbes, who had published his work about a century earlier, Rousseau argues that it was the act of entering into civil society itself that corrupted man. Men were not jealous or given to brutality, he argues, before they established society, and particularly before they established private property. According to Rousseau, a "savior of man" would have said centuries ago that:
Be sure not to this imposter; you are lost, if you forget that the fruits of the earth belong to us all, and the earth itself to nobody.
One of his salient points is that divisions in society (the title of the Second Discourse is actually Discourse on Inequality) should not be ascribed to anything about human nature, but rather were artificially created by society itself. With this in mind, we can better understand Rousseau's concept of society, and certainly political institutions. These ideas are not fleshed out in the Second Discourse, but in later works, especially The Social Contract. In that work, he claimed that sovereignty should not lie in the hands of a single person, but in the corporate body of the people. The power of the government, he thought, should be limited, and should always reflect the "general will," which he said should be asserted through assemblies elected by the people.