Modernism, in its broadest definition, is modern thought, character, or practice. More specifically, the term describes both a set of cultural tendencies and an array of associated cultural movements, originally arising from wide-scale and far-reaching changes to Western society in the late nineteenth and early twentieth centuries. The term encompasses the activities and output of those who felt the "traditional" forms of art, architecture, literature, religious faith, social organization and daily life were becoming outdated in the new economic, social and political conditions of an emerging fully industrialized world.

Modernism rejected the lingering certainty of Enlightenment thinking, and also that of the existence of a compassionate, all-powerful Creator. This is not to say that all modernists or modernist movements rejected either religion or all aspects of Enlightenment thought, rather that modernism can be viewed as a questioning of the axioms of the previous age.

A salient characteristic of modernism is self-consciousness. This often led to experiments with form, and work that draws attention to the processes and materials used (and to the further tendency of abstraction). The poet Ezra Pound's paradigmatic injunction was to "Make it new!" Whether or not the "making new" of the modernists constituted a new historical epoch is up for debate. Philosopher and composer Theodor Adorno warns us:

"Modernity is a qualitative, not a chronological, category. Just as it cannot be reduced to abstract form, with equal necessity it must turn its back on conventional surface coherence, the appearance of harmony, the order corroborated merely by replication."

Adorno would have us understand modernity as the rejection of the false rationality, harmony, and coherence of Enlightenment thinking, art, and music. But the past proves sticky. Pound's general imperative to make new, and Adorno's exhortation to challenge false coherence and harmony, faces T. S. Eliot's emphasis on the relation of the artist to tradition. Eliot wrote:

"[W]e shall often find that not only the best, but the most individual parts of [a poet's] work, may be those in which the dead poets, his ancestors, assert their immortality most vigorously."

Literary scholar Peter Childs sums up the complexity:

"There were paradoxical if not opposed trends towards revolutionary and reactionary positions, fear of the new and delight at the disappearance of the old, nihilism and fanatical enthusiasm, creativity and despair."

These oppositions are inherent to modernism: it is in its broadest cultural sense the assessment of the past as different to the modern age, the recognition that the world was becoming more complex, and that the old "final authorities" (God, government, science, and reason) were subject to intense critical scrutiny.

Current interpretations of modernism vary. Some divide 20th century reaction into modernism and postmodernism, whereas others see them as two aspects of the same movement.