Which was the most important concept in the enlightenment?

Scientists, literary men, and thinkers believed in the supremacy of reason. They demanded practical changes against injustice and so that people were considered as equal. They often attacked the government, the church, and the judicial systems of their country.

I consider Montesquieu's theory very important. He claimed that the judicial, executive and legislative branches of government should be separated.

I also found Rousseau's Social Contract one of the most important theories. He described a society in which each person could keep personal freeedom while at the same time behaving as a loyal member of of a community. =freedom is obedience to law. He also demanded the social equality of human beings.