David Hume

Scottish philosopher who pushed empiricism to its skeptical limits, arguing that reason cannot justify belief in causation, induction, the external world, or a persistent self — and developed a sentiment-based moral philosophy.

Custom and habit, not reason, ground our belief in causation. The problem of induction: no amount of past experience logically justifies future prediction. The self is not a substance but a bundle of perceptions. Moral judgments express sentiments (approval/disapproval), not rational truths. Is-ought gap: no descriptive statement entails a normative one.