Toleration vs. Tradition
Even though the new emphasis on reason was based on a very strong belief in God, it upset many Catholics, Protestants, and Anglicans who feared that if everyone were encouraged to use reason, most people would commit errors and sin. The clergy, these opponents argued, was necessary to provide moral and spiritual leadership for the rest of society.
Furthermore, these critics felt that Descartes' emphasis on reason would diminish the importance of tradition the way things had always been done and leave people without a proven way of doing things. Moreover, these critics opposed the idea of toleration, such as Locke had proposed, because they did not believe that people of different religions could co-exist peacefully.
The Enlightenment,therefore, is best understood as a movement to promote reason against tradition and to promote toleration against the necessity that everyone conform to the same beliefs.
Supporters of the Enlightenment used the term superstition to describe any belief they considered to be based not on reason but tradition including the teachings of the clergy, especially in the Catholic Church. These supporters also used the term fanatics to describe those who opposed toleration.