Isaac Newton's revolutionary theory of physics upended Aristotle's purpose-driven view of causation, and offered a new hope that we could finally obtain genuine scientific knowledge of the universe. But in a cruel twist of fate, a mysterious intellectual named David Hume emerged from the darkness of Scotland and struck at the heart of Newton's rebellion. Hume's arguments seemed to prove that humans could never find rational justification for any claims of scientific knowledge. Human reason, said Hume, was merely a slave to passions and custom.