Rousseau first lecture
A. The Preface:
1. On human nature, a divergence from (e.g.) Hobbes. As in Hobbes, "natural" is (mostly at least) opposed to "social" (so "social" belongs with "artificial"). But in Hobbes, human nature is a motivational directedness still operative in social life. The difference society makes is just that it channels the motivational directedness that human nature is in different directions, exploiting fear of sanctions. In Rousseau, the idea of human nature is the idea of what human beings must have been like in the remote past, before there was society; we aren't like that now. – The idea of nature easily acquires a different use, as at p. 68: "it is no light enterprise to separate that which is original from that which is artificial in man's present nature." Man's present nature is what human beings are like now, and his point is that that is largely artificial, a product of socialization. Human nature in this sense isn't natural in the first sense. It's the result of a historical development that began with human nature in the first sense.
2. Two elements in human nature (in the first sense): (1) concern for one's own wellbeing and preservation; (2) aversion to seeing others suffer. (Compare Hobbes, chap. VI, on pity. In Hobbes concern for others figures only as an offshoot from concern for oneself, whereas in Rousseau it's self-standing.)
B. The Preamble (pp. 77-9):
1. The book's topic is to be moral or political inequality, i.e. inequality that rests on a convention – not natural or physical inequality.
2. Understanding moral inequality requires going back to the state of nature (before there were conventions, so before there was moral inequality). Previous thinkers have tried to do this, but erred in reading back into human beings before society features that are indeed found in human beings as they are now, but which are due to society, not to human nature. (Consider this as directed against Hobbes.)