By the end of the nineteenth century, a late-modern outlook had emerged that challenged the Enlightenment tradition. One feature of this outlook was irrationalism. Rejecting Enlightenment values and Christian morality, Nietzsche envisioned a heroic individualism. In terms that would inspire fascist thinkers, Nietzsche extolled the unfettered will as the means of authentic self-creation. Dostoevski also embraced the irrational will, claiming that individuals must follow their own desires rather than be defined by external standards and values. Against positivism, Bergson raised intuitive experience, arguing that excessive reliance on reason turned individuals into mechanisms. Sorel politicized the irrational through his myth of general strike through which the proletariat would destroy decadent bourgeois society. Freud acknowledged the irrational core of human nature, but rather than celebrate it, he strove to control it through scientific analysis. Such analysis would, he hoped, preserve civilization from the unconscious drives that threatened it.

This period saw the rise of sociology as a discipline. A founder of the field, Durkheim studied the effects of modern individualism, the weakening of traditional social ties in place of which a new rational secular morality must be built. An intellectual forbearer of fascism, Pareto divided society into the elite and the masses, arguing that the elite must rule the irrational masses through cunning and violence. Le Bon's study of crowd psychology and discussion of how to manipulate it also influenced fascist thinkers. For Weber Western civilization, shaped by the Protestant ethic, had created a disenchantment of the world, a rationalization that enabled the rise of impersonal, oppressive bureaucracies. Weber also studied the charismatic leader who embodied the irrational forces of social life, emerging during times of crisis to rally people to a sacred mission.

In the arts, modernism overturned Renaissance modes of expression. Rejecting classicism and realism, artists in every medium turned from the representation of objective reality. Instead they explored the irrational and subjective experience, employing innovative techniques such as literary stream of consciousness and musical dissonance. In painting, modernism began with impressionism, the practitioners of which worked to capture the fleeting effects of light on objects. The postimpressionists went further, subordinating actual appearances to the requirements of form, and exploring the expressive possibilities of color and non-Western art. The expressionists in Germany and the fauves in France experimented even more radically with color as an expressive medium. To represent multiple points of view at once, Picasso and Braque pioneered cubism, a style Picasso developed further to shatter thoroughly the Renaissance tradition. Mondrian refined cubism into pure abstraction, an end Kandinsky also reached as he strove to represent private experience through color.

Modern physics overturned the Newtonian tradition by revealing the chaos inherent in the structure of the universe. Early insights into atomic structure culminated with Planck's quantum theory. Building on this theory, Einstein, Bohr, and Heisenberg theorized the fundamental uncertainty at that governed the operations of matter, space, and time, an uncertainty that could not be explained by Newtonian laws. Along with the major currents in philosophy, social thought, and art, modern physics contributed to the larger sense of cultural disorientation that distinguishes this period. This disorientation was a symptom of the disarray in to which the Enlightenment tradition had fallen, a disarray that would explode in the disastrous upheavals of the twentieth century.