By the end of the 1700s AD, Germany was beginning to be a more powerful country. France was busy with the Revolution, and the next important European philosopher after Rousseau came from Germany: Immanuel Kant.
Unlike earlier philosophers, Kant never traveled more than ten miles from his home in Prussia. When he was eight, he went to boarding school. His mother died when he was 13. In college, he learned about Newton's work. But like all the other Enlightenment philosophers, Kant never married or had children.
Kant started his work as an astronomer. He figured out that our solar system formed from a cloud of dust, and that large nebulas were made of thousands of stars.
Kant built on Descartes' idea that we can only know what we ourselves think, and what our senses tell us. Hume wanted a firm line between imagination and fact. Kant pointed out that even when our senses report facts, we can only understand them by thinking about them. You need both the facts and the thinking to understand the world.
Even though he wanted to use reason and rejected organized religion, Kant still allowed for the possibility that there was a God.