How did enlightenment thought contribute tot he start of the French Revolution?

The first French revolution was a revolution of the young against the Ancien Regime. They were motivated by reason and rationalism, humanism, all products of the Enlightenment that directly opposed the Absolute Monarchy of France.

Ironically, other than the Great Earthquake of Lisbon, one of the key events that sparked the Enlightenment was the Sr Bartholomew's day Massacre.