sex
In the paragraphs below Rousseau acknowledges that there is a realm of life (i.e. that which "does not relate to sex") in which men and women are basically equal. In everything that "does relate to sex," however, they are not equal, and he suggests that there are more differences between men and women that relate to sex than we are generally willing to acknowledge.
In much of what follows Rousseau provides the reader with an essentialist view of the manifest differences between men and women. In today's parlance, one might say that he stresses "sex" rather than "gender"in his analysis of social difference. Indeed modern readers (and many of Rousseau's contemporaries and near contemporaries, including most notably Mary Wollstonecraft) have suggested that Rousseau commits the error that he criticized Hobbes and others of committing i.e. that he presumes as "natural" that which is in fact the result of generations of socialization and control. In Rousseau's defense one could say that in line with his purpose of creating a companion for Emile, Rousseau will make Sophie into a woman who complements him rather than competes with him. Whether or not Rousseau ends up maligning women in the process remains an open question.