The assertion that physical man is just another animal is very important. It goes against the classical and Biblical view that man, by his very nature, possesses qualities that set him apart from animals. The distinction between human and animal was used both to justify man's possession and use of the Earth's resources, and to explain why humans apparently have certain unique capabilities, such as reason and language. Rousseau's definition of man answers the second point very cleverly; man is like but yet unlike other animals, because of the unique way he develops. He does not argue that modern man is similar to an orangutan, but that he once was, before human development changed him.
The meaning of the Aristotle quote at the beginning of the book ("What is natural has to be investigated not in beings that are depraved, but in those that are good according to nature") becomes apparent as you look at Rousseau's treatment of natural man. The importance of looking at man as he really is means that one must begin with the most basic part of his nature: his physique. Once the physical strength and senses of natural man have been established, Rousseau can consider his more complicated functions.
"Metaphysical" or "moral" man for Rousseau covers what we would now call human intelligence and the higher functions of the brain. It is here that Rousseau explains exactly what distinguishes man from animal. Both are essentially mechanical, but man has the ability to act freely, which allows him to choose, and to vary his behavior. More importantly, humans have the faculty of perfectibility. Interpretations of this important quality vary, but it is most helpful to see it as a capacity for change, or an ability to be molded by one's environment. Man cannot only choose, he can also change rapidly, and develop at an almost unlimited rate. Without this quality, humans would remain in the state of nature forever, and never progress beyond the level of other animals. Rousseau is clear that this can be a tremendously positive force. We should admire the tremendous distance that humans have covered, but also despair of the state to which it has brought us. Rousseau does not contradict himself when he says that perfectibility is the source of both enlightenment and vice. It is because perfectibility produces both that perfectibility can account for human development.
The mechanism by which perfectibility operates is unusual. Rousseau argues that the passions produce reason in man, by producing needs that require him to think in order to satisfy them. Linking reason and the passions goes against the philosophical tradition, beginning with Plato, that sees the two as fundamentally opposed. For many other philosophers, reason should rule the passions, or vice versa. But Rousseau's argument works. The passions are strong feelings that move us to act, or to reach beyond ourselves, and if reason is something that humans were not created with, then some force must have made men reach out towards reason. For Rousseau, this force was need, which stimulated certain passions in mankind, then caused men to act and develop. It is a giant leap from the passions to the development of reason, and one that works only if you assume that the passions exist prior to reason.
Rousseau separates language and reason, a division that breaks with the view inherited from Plato and the Greeks that speech and reason are both represented by the word "Logos." Rousseau wrote extensively on language in other works, including the Essay on the origin of languages, so his account here is relatively brief. It is clear that at a central part of reasoning—abstract thought—is impossible without language. Therefore reason and language are very closely linked. Abstract concepts, such as romantic love, jealousy, or reason, exist for Rousseau only when men have the right words to describe them. Rocks, trees and other physical things exist independently of language because they are real. Therefore savage man cannot have complex thoughts until the development of language.
Rousseau's discussion of sociability follows on from his treatment of language. His argument against Hobbes is important here. Hobbes's position, described in Leviathan, is that the state of nature is a state of war between humans. Mankind's passions drive him to desire things and to fear others. This leads to bloody conflict. Although he agrees with Hobbes that man is not naturally sociable, Rousseau also believes that he is naturally peaceful. The problem with Hobbes's account is essentially the method he uses. Hobbes looks at man deformed by society, and calls him natural man. Really, he should attempt to follow Rousseau and look back at man's origins.
Rousseau's idea of the natural goodness of savage man rests not on any good quality that man might have, but rather on his ignorance. Without language or the ability to reason, it simply never occurs to the savage to be evil. This clearly conflicts with the Biblical idea of original sin, which states that man is born bad and can only be redeemed through God's grace. Such an idea is nonsensical to Rousseau, who argues that any idea of savage man as evil comes from confusing savage and civil man. From his picture of savage man, Rousseau derives the two basic principles of the Discourse: pity and self- preservation. The two qualities are what make it possible for savage men to exist together, because they essentially balance each other out. Pity draws one person towards another, whereas the desire for self-preservation draws men apart. These two principles rarely conflict, according to Rousseau, because one person's pity should prevent him from interfering with another's attempts to preserve himself. The reference to Mandeville shows how important Rousseau felt pity to be: Mandeville controversially argued for the doctrine of "private vices, public benefits." His position was seen as extreme by many, so the fact that he endorsed pity is proof for Rousseau of its universality. Rousseau goes further than Mandeville by arguing that pity was the only rule that natural man needed. Pity takes the place of laws because if you pity another and empathize with him, you cannot harm him. In the civil state, however, laws develop, in part because self-preservation and pity are no longer balanced against each other. Amour propre is a kind of extreme self-preservation unbalanced by pity.
Only self-preservation and pity can guarantee a degree of harmony. Rousseau is clear that ordinary laws cannot have this effect, partly because they rely on reason. Also, laws may in fact create certain evil passions. This is an unconvincing version of the chicken-and-egg argument. Rousseau intends to suggest that if savage man can be good without laws, then perhaps only laws make him bad. However, if this is true, then why are laws introduced? Rousseau attempts to answer this in Part Two.
Many writers have interpreted this section as describing the "noble savage." Such interpretations argue that savage man is naturally good and virtuous, and that Rousseau really wants his readers to emulate this model and return to the primeval forests. This is far from Rousseau's point, however. Firstly, Rousseau makes it very clear that talking about natural goodness is a mistake; secondly, there is very little "nobility" in natural man. He is merely an animal, without any higher faculties or interest in anything other than food, rest and sex. Thirdly, it is clear that the Discourse sets out a model of development that cannot be reversed. Rousseau may admire some aspects of the savage's life, or even think that he is better off than modern man, but he never considers that we could or should return to the state of nature.
Rousseau's conclusion to this section restates and develops his central argument, but leaves several questions hanging. The main question to be answered is how inequality develops from the basic state of nature presented here.