Idealism is a philosophy that positions itself against the materialist philosophy. While materialists (like Thomas Hobbes) believe that the only way to decode society and social morality is through imperically acknowledged truths. Idealism posits that the only confirmed truth is the existence of ideas. Emanuel Kant was a classic idealist. In his discussions of a priori filters, phenomena/noumena, he dismisses the conjecture that imperical truth exists, based on the notion that all individuals process their imperical observations through a set of a priori filters which all humans share. He goes on to assert that there are two realities: the noumena ("things in themselves"), or the tangible imperical reality, and the phenomena, or the way that human beings percieve reality.

These approaches to Enlightenment thinking, materialism and idealism, divided many of the most important theorists of the age into two schools, creating a discourse that was eventually interrupted by Georg Wilhelm Friedrich Hegel's theory of sublation, and then later by Karl Marx's dialectical materialism.