How did Rousseau differ from Voltaire? Rousseau was a French philosopher in the 1700s, while Voltaire was a French monarch in the 1600s. Rousseau was a French monarch in the 1600s, while Voltaire was a French philosopher in the 1700s. Rousseau argued against inequality among the classes, while Voltaire argued for freedom of speech and religion. Rousseau argued for freedom of speech and religion, while Voltaire argued against inequality among the classes.