In the 19th century, the philosophers of the 18th-century Enlightenment began to have a dramatic effect on subsequent developments in philosophy. In particular, the works of Immanuel Kant gave rise to a new generation of German philosophers and began to see wider recognition internationally. Also, in a reaction to the Enlightenment, a movement called Romanticism began to develop towards the end of the 18th century. Key ideas that sparked changes in philosophy were the fast progress of science, including evolution, most notably postulated by Charles Darwin, Alfred Russel Wallace and Jean-Baptiste Lamarck, and theories regarding what is today called emergent order, such as the free market of Adam Smith within nation states, or the Marxist approach concerning class warfare between the ruling class and the working class developed by Karl Marx and Friedrich Engels. Pressures for egalitarianism, and more rapid change culminated in a period of revolution and turbulence that would see philosophy change as well.

With the tumultuous years of 1789–1815, European culture was transformed by revolution, war and disruption. By ending many of the social and cultural props of the previous century, the stage was set for dramatic economic and political change. European philosophy reflected on, participated in, and drove, many of these changes.

The last third of the 18th century produced a host of ideas and works which would both systematize previous philosophy, and present a deep challenge to the basis of how philosophy had been systematized. Immanuel Kant is a name that most would mention as being among the most important of influences, as is Jean-Jacques Rousseau. While both of these philosophers were products of the 18th century and its assumptions, they pressed at the boundaries. In trying to explain the nature of the state and government, Rousseau would challenge the basis of government with his declaration that "Man is born free, but is everywhere in chains". Kant, while attempting to preserve axiomic skepticism, was forced to argue that we do not see true reality, nor do we speak of it. All we know of reality is appearances. Since all we can see of reality is appearances, which are subject to certain necessary and subjective forms of perceptions, Kant postulates the idea of an unknowable (while at the same time limiting our use of science and the principle of causality to the appearances). Hegel's distinction between the unknowable and the circumstantially unknown can be seen as the beginnings of Hegel's rational system of the universe.

Yet another philosopher of the late Enlightenment that was influential in the 19th century was Pierre-Simon Laplace (1749–1827), whose formulation of nomological determinism is famous up to this day.

This is a partial list of schools of 19th-century philosophy (also known as late modern philosophy).

One of the first philosophers to attempt to grapple with Kant's philosophy was Johann Gottlieb Fichte, whose development of Kantian metaphysics became a source of inspiration for the Romantics. In Wissenschaftslehre, Fichte argues that the self posits itself and is a self-producing and changing process.

Friedrich Wilhelm Joseph Schelling, a student of Fichte, continued to develop many of the same ideas and was also assimilated by the Romantics as something of an official philosopher for their movement. But it was another of Fichte's students, and former roommate of Schelling, who would rise to become the most prominent of the post-Kantian idealists: Georg Wilhelm Friedrich Hegel. His work revealed the increasing importance of historical thinking in German thought.

Arthur Schopenhauer, rejecting Hegel and also materialism, called for a return to Kantian transcendentalism, at the same time adopting atheism and determinism, amongst others. His secular thought became more popular in Europe in the second half of the 19th century, which coincided with the advents of Darwinism, positivism, Marxism and philological analysis of the Bible.