Philosopher David who wrote "A Treatise of Human Nature"

HUME

["This Scottish Enlightenment thinker famously argued that reason alone cannot justify causation and was a key figure in skepticism about induction."]

This clue points to the 18th-century Scottish philosopher David Hume, best known for his foundational work "A Treatise of Human Nature." The answer is simply his last name, "HUME," which fits the crossword’s letter count. No wordplay is involved—it’s a direct reference to his famous text on human cognition and morality. If you’ve studied philosophy, his name likely stands out immediately.