The Scientific Revolution had a major impact on ideas about how people should be governed.  It promoted the idea that the physical world should be understood through science and rationality.  By extension, Enlightenment thinkers came to believe that scientific and rational thought should be applied to issues of human society as well.

The Scientific Revolution was based largely on the idea that the physical world should be understood through reason.  Scientists should look at the world as it was and apply reason to their observations instead of relying on the authority of the Church or of Aristotle.  The Scientific Revolution held that, as Descartes argued, people should only accept things that reason told them were true.

This idea was applied to how human beings should be governed.  Enlightenment thinkers did not believe that it was rational to think that God had appointed kings to rule over them.  They felt, instead, that God had given them rationality that they should use to rule themselves.  They felt that God had given them rights that governments should respect.  In short, they argued that reason told them that a more democratic and liberal system was the best system for governing human beings.