The Scottish philosopher David Hume developed the concept of "mitigated skepticism," which remains a viable alternative to the systems of rationalism, empiricism, and idealism. Hume raised relevant issues and arguments that remain central to contemporary thought, but his philosophical writings went unnoticed during his lifetime. The considerable fame he achieved derived from his work as an essayist and historian.

Hume was born on April 26, 1711, near Edinburgh. A second son, he was not entitled to a large inheritance, and he failed careers in law and business because of his "aversion to everything but the pursuits of Philosophy and general learning." Until he was past forty, Hume was employed only twice.

The first two volumes of his major philosophic work A Treatise of Human Nature were published in 1739 and the third appeared in the following year. Book I of the Treatise was recast as An Enquiry Concerning Human Understanding and...