Søren Aabye Kierkegaard (1813–1855) was an astonishingly prolific writer whose work—almost all of which was written in the 1840s—is difficult to categorize, spanning philosophy, theology, religious and devotional writing, literary criticism, psychology and social critique. Kierkegaard’s mode of philosophizing opposes system-building and owes more in its approach to the ancients, particularly his hero Socrates, though his work also draws strongly and creatively on the Bible and other Christian sources.