According to the “Preface,” Rousseau sees that men are as naturally equal among themselves as the individuals of various other animal species: but how equal are the other animal species? Not very, they have rank ordering. Rousseau is seeking to clarify the question of human equality and he tells us that he is not sure he has the answer despite having spent so much time thinking about it. This should give you pause about those who claim to know. What is necessary for us to come to know, to come to understand human nature and in what sense human beings are equal?
Rousseau asks, “What experiments would be needed in order to come to know natural man; and by what means can these experiments be performed within society?” That is, how can we test knowledge of nature and nurture in society?