Jean-Jacques Rousseau, answered from the texts and cited to the page.
Man is naturally good. This is the foundational claim of the entire authorship, stated as the opening of Émile — everything is good as it leaves the hands of the Author of things; everything degenerates in the hands of man — and demonstrated in the hypothetical genealogy of the Second Discourse. In the original state of nature, prior to the institution of property and the consolidation of comparison, the human animal lives by two passions only: amour de soi, the natural concern for one's own preservation and well-being, which has nothing comparative or competitive in it; and pitié, the natural repugnance at seeing another sensitive being suffer, the source of all the social virtues before they have names.123
There is no malice in the natural human being, no envy, no vanity, no domination — these belong not to nature but to a particular history. The genealogy of inequality is the history of how amour-propre (the comparative form of self-love) emerged from the conditions that taught human beings to compare themselves with one another, of how property formalized the dependence that comparison produced, of how the chains that bind master and slave alike were forged stage by stage from the first hut to the first deed to the first written code.
The vice is not in human nature; it is in the history that human beings, with their fatal perfectibilité, made of themselves.45
I have shown that all the vices imputed to the human heart are not natural to it; I have stated the manner in which they are born. I have followed their genealogy, so to speak, and I have shown how, through continuous deterioration of their original goodness, men finally become what they are.Letter to Beaumont, p. 60
Mollissima corda Humano generi dare se natura fatetur, Que lacrimas dedit." Second Discourse (Pl., III, 153-156) 7 Mandeville sensed very well that even with all their morality men would never have been anything but monsters if Nature had not given them pity in support of reason; but he did not see that from this quality alone flow all the social virtues he wants to question in men.Discourse on the Origins of Inequality, p. 69
If moral goodness is in conformity with our nature, man could be healthy of spirit or well constituted only to the extent that he is good. If it is not and man is naturally wicked, he cannot cease to be so without being corrupted, and goodness in him is only a vice contrary to nature.Emile, or On Education, p. 294
How many times have these hands felt the tears I shed on them! The young couple share my raptures, and they too are moved. Their respectable parents once again enjoy their youth in that of their children. They begin, so to speak, to live again in them—or rather they come to know the value of life for the first time. They curse their former wealth which prevented them from tasting so charming a fate at the same age.Emile, or On Education, pp. 487–491
He was even less able to count to five; and although, placing his hands on one another, he could have noticed that the fingers corresponded exactly, he was very far from thinking of their numerical equality.Discourse on the Origins of Inequality, pp. 123–124
The doctrine has been continuously misread as romantic primitivism — the noble-savage caricature, the idea that the agent recommends a return to the forest, the idea that civilization is mere fall. This is not what the Second Discourse argues. The state of nature is a hypothetical reconstruction, not a historical destination; the genealogy is a diagnostic, not a counsel of withdrawal; the constructive program of Émile and the Social Contract shows that humans retain natural goodness as something the right education and the right political form can develop rather than corrupt. The Augustinian original-sin frame the Letter to Beaumont responded to is the principal historical alternative the position explicitly refuses.