Summary
Rousseau's essay was written for a prize competition held by the Academy of Dijon, asking the question: what is the origin of inequality among people, and is it authorized by natural law? But Rousseau opens by stating that he is not going to answer the questions directly. Instead, he's going to answer a broader question that will ultimately lead to the more specific answer. The broader question is: what is man?
Because man is so deformed by cultural and by the institutions of society, Rosseau says, in order to get a good sense of him we'll have to imagine him as he is in nature. This presents two problems. First, there is the difficulty of disentangling which aspects of man are natural, and which are socially conditioned. Second, if we don't know what nature and law are, how can we know for certain if natural law has "authorized" inequality? This would seem to be a contradiction in terms anyway, since laws are given rationally, while to be natural it has to speak with the voice of nature, as Rousseau puts it.
Rousseau identifies two aspects of human character that he believes have not been deformed by culture. The first is the desire for self-preservation, which he believes is common to all natural creatures. The second is that of pity. These are the basis for all of man's later development. We pity the suffering of other human beings not from reason, but from our feelings, which precede rational thought. Feelings bind human beings together before institutions do. Thus animals are not subject to natural law, because they have no reason. But they are subject to natural right, because they are objects of pity, and because they feel. Animals have the right not to be abused by human beings.
So, by getting a picture of man as he actually is, it is easier to answer questions about what is changeable and what is unchangeable, what is intended for him and what he brought on himself. Otherwise, there can be no study of modern society.
Analysis
It is worth noting that, though Rousseau made his reputation with an essay called "The Discourse on Arts and Sciences," for an earlier contest held by the Academy of Dijon, which won the prize, this time Rousseau did not actually enter his essay into the contest. Instead, he took the prompt as a jumping-off point for a larger consideration about the nature of man—which would have been far too long for the essay requirements—and had it published on his own. This bit of context gives us a sense of how Rousseau fit into the philosophical debates of his time. Though he was widely read, he resisted many of the formal and institutional practices of his time, in order to engage in what he felt were deeper and more substantial reflections.
The preface also gives us a sense of how Rousseau fit into some of the major debates of his time, especially that of natural law. Though the concept has deep roots going back to Greek antiquity, Rousseau's main interlocutor here is the English philosopher Thomas Hobbes. Hobbes considers the possibility that there are rights human beings have just by virtue of being human: the right not to suffer physical harm, for example. (This language and line of thinking strongly influenced the American Constitution, with its emphasis on "self-evident truths.") Natural laws are consciously dictated laws based on these principles, like the command to avoid harming others wherever possible.
Typically for Rousseau's argumentation, rather than staying in the terms of the debate on natural rights, he is much more interested in the difficult question, "what is nature?" What does it mean to act naturally? Self-preservation and pity answer this question in two ways. First, it explains the push and pull between inwardness and sociability in man. And second, it argues that the basis of society is not rational, and cannot be determined rationally, but is ultimately based on feeling.
This question goes beyond the terms of the essay contest and will become the cornerstone of Rousseau's ethics, as well as his autobiography. We are happy when we act according to our natural impulses, our conscience; we are unhappy when we accept duties, obligations, and even privileges that we consider inauthentic. The search for an "authentic" life, in accordance with the principles of nature, would be hugely influential especially in the German arts, in the work of J.W. Goethe, Friedrich Schiller, and the Romantic movement, who saw art as a tool for imagining such a life.
