Rousseau begins by twisting the prize question towards his own particular agenda. The original question concerns what is the nature of inequality among men, and whether it is authorized by the natural law. Rousseau asks another, related question: how can one know inequality without knowing man? To answer this question we must not consider man as he is now, deformed by society, but as he was in nature. Progress drives man as a species further from its original condition in the state of nature. As knowledge increases, so our ignorance of the true nature of man increases.
Rousseau acknowledges the hypothetical and conjectural nature of what he is about to do in the Discourse. Undertaking to disentangle the natural from the artificial in man is a difficult task indeed. What is needed is a kind of experiment to achieve this. At the moment, ignorance of the nature of man casts uncertainty over the nature of natural right. Rousseau provides a brief account of the ancient and modern debate over natural rights and natural law.
A second problem arises; if we are uncertain about what the terms nature and law mean, how can we define the natural law that is supposed to authorize inequality? In considering this question, we return to the problem of the real nature of man. For if we are ignorant of man's nature, it is impossible to tell whether the definition of natural law we decide on fits with that nature at all. To be a law, it has to be agreed to "knowingly" (rationally), and to be natural it must "speak with the voice of nature."
There is a way out of this problem, however. Rousseau next claims that he perceives two basic principles that exist "prior to reason"—that is, before man is deformed by society and rationality. These are self-preservation and pity. From these principles, which do not require sociability, natural right flows. Man's duties are not dictated to him by reason alone, but by self-preservation and pity. Therefore a man will not harm another sentient (pain-feeling) being unless his own self-preservation is at stake. The duty not to harm others is based not on rationality but on sentience, the state of being able to feel. According to Rousseau, this solves the age-old question of whether animals participate in natural law. As they are not rational, he says, animals cannot have any part in a natural law, but as sentient beings they take part in natural right, that is, they feel and are the subjects of pity. This gives animals at least the right not to be mistreated by man.
The study of natural man, of his "true needs" and "fundamental principles of his duty," is the only way to clear up important issues such as the origin of moral inequality and the foundations of the "body politic" (the state). Without such a study, the foundations of modern society seem shaky and insecure, and it is hard to separate what "divine will" intended from what man himself created. By realizing what we would have been if left to ourselves, Rousseau argues that we can better appreciate "him whose beneficient hand" steered us away from the worst disorders.
The Preface was probably written for the published version of the Discourse, and is essentially Rousseau's attempt to define the problem he is about to tackle. He makes his methodology and assumptions clear at the beginning of the work, and shows some of the problems with the terms he uses. His first move is an important one: shifting the focus of the question towards the nature of man gives the Discourse added depth. All questions about inequality and modern society depend on one question: what is natural?
The context of natural rights and natural law theories is very important to understanding what Rousseau is doing. The two, related debates are complex, and began with ancient and medieval thinkers. Among the more recent thinkers that Rousseau refers to, Hobbes and Grotius are the most important. Essentially, a natural right is a claim that all people have over others by virtue of being human, such as a right to have, or to do, something. Natural rights are not granted or instituted by society, but are created by God or Nature. Similarly, natural laws are rational regulations that compel all people to act in a certain way, and are generally seen as commands from God or Nature to be obeyed by man. Hence the prize question Rousseau is answering is about whether God or Nature commands that people should be unequal. An example of a natural law is the command to seek peace with other people at every opportunity whereas an example of a natural right is the right to self-preservation. Natural right and natural law are not interchangeable, but together were often seen as providing a basic framework of rights and duties that could be used to found a political society. The point is to avoid conflict by establishing an uncontroversial basis for people to join together. However, as Rousseau points out, no one can agree on what rights and duties were natural or basic. The second problem is that modern thinkers believe that only a rational creature can have natural rights. This represents a raw deal for the animals, but also a problem for Rousseau, who goes on to argue that natural man and animals are, in fact, alike.
Rousseau's key point is that natural rights and laws mean nothing if we do not understand the nature of man. There must be a correlation between the two for natural laws to mean anything. Therefore, to understand what this nature is, we have to take reason out of the equation entirely, as man in his original condition may not have been a rational creature. We need basic concepts, or principles, on which to base a theory of man—concepts that have nothing to do with reasoning. In designating self-preservation and pity as these principles, he selects two apparently conflicting concepts. The desire to preserve one's own life is a standard of natural rights theories, discussed by both Hobbes and Grotius, but pity is a more novel concept. Whilst one principle pulls man towards others, the other directs him towards himself. Rousseau argues that there is no contradiction between the two. This is a key theme that will be developed later in the Discourse.
Also important is the reference to the natural rights of animals. Rousseau argues not that animals have all the rights that humans do, but only that to harm another sentient creature is universally wrong. It introduces a central point made in Part One of the Discourse, that man in his natural state is merely an animal, and shares all of an animal's central characteristics.