the answers.Philosophes believed that natural law—not the hand of God—explained the universe. Understanding could be achieved through the use of mathematics, science, and philosophy, rather than Christian faith. Deism replaced religious theology.

After the French Revolution of 1789, the Catholic Church was persecuted. Many priests were killed, and scores of churches were closed. The Cult of Reason replaced the Catholic Church.

In 1787, Enlightenment thought influenced America's Founding Fathers in their decision to separate church and state. The Founding Fathers knew about the terrible religious wars that had occurred in Europe, and they were determined to create a secular state.

During the Enlightenment, people started to look for rational explanations for why things happened. This is a sharp contrast with the Middle Ages, when most natural phenomena was believed to be caused by the direct action of God. During the Enlightenment, people started to question giving the Church exclusive power over one's soul, and many people started reading the Bible and looking for their own interpretations. This led to the Protestant Reformation. Scientists also took part in the Enlightenment, as they used the scientific method and direct observation to explain natural occurrences. This led to advances in science and medicine. While superstitions still existed, they were less common in classes exposed to secular education.

The Enlightenment also spread to government. People started to question the divine right of kings. This would lead to a surge in people longing to govern themselves, either by creating a republic or making a monarch subservient to a legislative body. This was perhaps the greatest legacy of the Enlightenment, as people did not put all of their trust in a leader who was to enact God's will on Earth and govern everything outside of the Church's jurisdiction.

Descartes is often called the father of modern philosophy and, in his Meditations on First Philosophy, he set the groundwork for the secularism of the Enlightenment.

In that work, Descartes sought to find a ground for knowledge. He found it by throwing out anything that he could doubt. This included Church doctrine. He grounded knowledge in his certainty that "I think, therefore I am." From that rational starting point, he reasoned his way into a belief in the existence of God, which he equated with perfection.

In doing so, Descartes put reason ahead of religious authority. This was a reversal of how people had thought in the Middle Ages. Before Descartes, people had grounded reason in the authority of received religious truth.

Separating reason from religion and giving reason primacy was key to Enlightenment thinking and led to secularism, because now religious truth could be questioned and doubted. Religious truth now how to justify itself in terms of reason and not vice-versa.

The Enlightenment promoted a more secular outlook in society by encouraging people to question received authority.

In Medieval times, people tended to accept ideas that came from authority figures.  These could be figures from the past, like Aristotle, whose ideas were widely believed and taken on faith.  These could also be people like church figures.  The Enlightenment encouraged people to believe only in things that could be proven.  This led to a more secular outlook in society as people stopped looking to the church for answers and instead turned to science for answers that could be backed up by empirical proof.

Secularism had a major impact on society during the Enlightenment. Whereas Europeans unified behind their faiths before, secularism led to the rise of the state and nationalism. People began to feel more strongly about their national and local leaders than they did about religious leaders who lived far away.

Secularism also led to increased skepticism. People looked for rational reasons to explain phenomena. Instead of stating that everything that happened was the will of God, people started to look for measurable causes that had measurable effects. While some people used the new emphasis on science to turn away from God, others (the Deists) were able to compartmentalize their faith in God with their faith in science by having the idea that God was like a watchmaker who put the Earth in motion eons previously and did not interfere with it. This allowed for an appreciation of science without a total rejection of religion.

Secularism was a major turning point in Western thought. It led to increased loyalty to the state as well as advances in science and philosophy. Many great ideas come from this period—most notably the concept that humans have fundamental rights.