The decades surrounding the First World War — from the 1880s to the 1930s — brought intense cultural and intellectual experimentation. As people grappled with the costs of the war and the challenges of postwar recovery, philosophers and scientists questioned and even abandoned many of the cherished values and beliefs that had guided Western society since the eighteenth-century Enlightenment and the nineteenth-century triumph of industry and science. Radical intellectuals dismissed the possibility that rational thought could lead to greater human understanding or social progress. Though some thinkers embraced Christianity, others rejected Christian teachings. Modern thought thus dovetailed with the ongoing political and social crises of the 1920s and 1930s.

Historians find it relatively easy to set precise dates for political events, such as the outbreak of wars or the outcome of national elections. Exact dates for the rise and fall of intellectual and cultural developments are more difficult to define. The emergence of modern philosophy, for example, did not follow the clear-cut timelines of political history. Thus to understand the history of modern thought, we must investigate trends dating back to the last decades of the nineteenth century and follow them into the 1950s.