Need is the key driving force behind modern society. Needs result from the passions, which make men desire an object or activity. In the state of nature, needs are simple and restricted to those that are necessary to human survival: food, rest, and sex. As societies and cooperation develop, however, men have more leisure time to fill. The result is a development of more and more needs, which gradually become necessities. Rousseau means things like socializing, exotic food, and entertainment. Although they are initially pleasurable, these new needs bind men together and shape their lives. Ultimately, needs control men and make them the slaves of others. When a man requires others to fulfill his needs, or simply the needs of other people, another can dominate him. Unnecessary needs are the foundation of modern inequality, according to Rousseau.

Rousseau's sustained analysis of this theme is a vital part of Discourse on Inequality. Like human nature, need is a concept that changes and becomes corrupt as man develops. The idea of a system of needs influenced Hegel's idea of civil society and should provoke reflection today. In an age of prosperity, consumer goods and the mass media, Rousseau's depiction of men who are enslaved to imaginary needs seems very apt.