Jean-Jacques Rousseau's critique of modern civilization is contained in two essays, "Discourse on the Arts and Sciences" and "Discourse on the Origins and Foundations of Inequality Among Men".
The common argument we see, which is materialist in nature, in both of his essays is that the fundamental human nature of individuals can be altered by the kind of society they live in. As Marx would later write, "It is the social being of man that affects their consciousness and not the opposite".
Rousseau can be, as we shall see, seen as a precursor to Marx. He can also be seen as a precursor to the entire field of critical theory if we rely on the definition that "critical theory is *any* approach to social philosophy that focuses on the critique of society and culture".