Jean Jacques Rousseau (1712-1778): Swiss-French philosopher, writer, political theorist, and self-taught composer
Rousseau contended that man is essentially good, a "noble savage" when in the state of nature (the state of all the "other animals", and the condition man was in before the creation of civilization and society), and that good people are made unhappy and corrupted by their experiences in society. He viewed society as "artificial" and "corrupt" and that the furthering of society results in the continuing unhappiness of man. Rousseau's essay, "Discourse on the Arts and Sciences" (1750), argued that the advancement of art and science had not been beneficial to mankind. He proposed that the progress of knowledge had made governments more powerful and crushed individual liberty. He concluded that material progress had actually undermined the possibility of sincere friendship, replacing it with jealousy, fear and suspicion.
Perhaps Rousseau's most important work is The Social Contract that describes the relationship of man with society. Contrary to his earlier work, Rousseau claimed that the state of nature is a brutish condition without law or morality, and that there are good men only as a result of society's presence. In the state of nature, man is prone to be in frequent competition with his fellow men. Because he can be more successful facing threats by joining with other men, he has the impetus to do so. He joins together with his fellow men to form the collective human presence known as society. The Social Contract is the "compact" agreed to among men that sets the conditions for membership in society.
Rousseau was one of the first modern writers to seriously attack the institution of private property, and therefore is considered a forebearer of modern socialism and Communism (see Karl Marx). Rousseau also questioned the assumption that the will of the majority is always correct. He argued that the goal of government should be to secure freedom, equality, and justice for all within the state, regardless of the will of the majority (see Democracy).
One of the primary principles of Rousseau's political philosophy is that politics and morality should not be separated. When a state fails to act in a moral fashion, it ceases to function in the proper manner and ceases to exert genuine authority over the individual. The second important principle is freedom, which the state is created to preserve. Rousseau's ideas about education have profoundly influenced modern educational theory. He minimizes the importance of book learning, and recommends that a child's emotions should be educated before his reason. He placed a special emphasis on learning by experience.
"Man is born free but everywhere is in chains."
“In reality, the difference is, that the savage lives within himself while social man lives outside himself and can only live in the opinion of others, so that he seems to receive the feeling of his own existence only from the judgement of others concerning him. It is not to my present purpose to insist on the indifference to good and evil which arises from this disposition, in spite of our many fine works on morality, or to show how, everything being reduced to appearances, there is but art and mummery in even honour, friendship, virtue, and often vice itself, of which we at length learn the secret of boasting; to show, in short, how abject we are, and never daring to ask ourselves in the midst of so much philosophy, benevolence, politeness, and of such sublime codes of morality, we have nothing to show for ourselves but a frivolous and deceitful appearance, honour without virtue, reason without wisdom, and pleasure without happiness.”
In 1762, Rousseau published The Social Contract, which, though it was largely unread when it first came out, became one of the most influential works of abstract political thought in the Western tradition. In the Discourse on Inequality, Rousseau had tried to explain the human invention of government as a kind of contract between the governed and the authorities that governed them. The only reason human beings were willing to give up individual freedom and be ruled by others was that they saw that their rights, happiness, and property would be better protected under a formal government rather than an anarchic, every-person-for-themselves type of society. He argued, though, that this original contract was deeply flawed. The wealthiest and most powerful members of society "tricked" the general population, and so installed inequality as a permanent feature of human society. Rousseau argued in The Social Contract that this contract between rulers and the ruled should be rethought. Rather than have a government which largely protects the wealth and the rights of the powerful few, government should be fundamentally based on the rights and equality of everyone. If any form of government does not properly see to the rights, liberty, and equality of everyone, that government has broken the social contract that lies at the heart of political authority. These ideas were essential for both the French and American revolutions; in fact, it is no exaggeration to say that the French and American revolutions are the direct result of Rousseau's abstract theories on the social contract. 
"Let us return to nature."  In his earlier writings Rousseau identified nature with the primitive state of savage man. Later, especially under the criticism of Voltaire, Rousseau took nature to mean the spontaneity of the process by which man builds his personality and his world. Nature thus signifies interiority, integrity, spiritual freedom, as opposed to that imprisonment and enslavement which society imposes in the name of civilization. Hence, to go back to nature means to restore to man the forces of this natural process, to place him outside every oppressing bond of society and the prejudices of civilization.