Hume conceived of philosophy as the inductive science of human nature, and he concluded that humans are creatures more of sensitive and practical sentiment than of reason. For many philosophers and historians his importance lies in the fact that Immanuel Kant conceived his critical philosophy in direct reaction to Hume (Kant said that Hume had awakened him from his “dogmatic slumber”). Hume was one of the influences that led Auguste Comte, the 19th-century French mathematician and sociologist, to develop positivism. In Britain Hume’s positive influence is seen in Jeremy Bentham, the early 19th-century jurist and philosopher, who was moved to utilitarianism (the moral theory that right conduct should be determined by the usefulness of its consequences) by Book III of the Treatise, and more extensively in John Stuart Mill, the philosopher and economist who lived later in the 19th century.

In throwing doubt on the assumption of a necessary link between cause and effect, Hume was the first philosopher of the postmedieval world to reformulate the skepticism of the ancients. His reformulation, moreover, was carried out in a new and compelling way. Although he admired Newton, Hume’s subtle undermining of causality called in question the philosophical basis of Newton’s science as a way of looking at the world, inasmuch as that science rested on the identification of a few fundamental causal laws that govern the universe. As a result, the positivists of the 19th century were obliged to wrestle with Hume’s questioning of causality if they were to succeed in their aim of making science the central framework of human thought.

For much of the 20th century it was Hume’s naturalism rather than his skepticism that attracted attention, chiefly among analytic philosophers. Hume’s naturalism lies in his belief that philosophical justification could be rooted only in regularities of the natural world. The attraction of that contention for analytic philosophers was that it seemed to provide a solution to the problems arising from the skeptical tradition that Hume himself, in his other philosophical role, had done so much to reinvigorate.