Metaphysics

German idealists attempted to preserve causal laws and other necessary truths about objects by emphasizing the role of the self in understanding objects. As the movement developed, figures such as Gottlieb Fichte (1762–1814) went further, arguing that, in a sense, the self creates objects.

Immanuel Kant (1724–1804), in his Critique of Pure Reason, defended the view, largely against Hume, that there are basic a priori laws, including causal laws, governing all objects of experience. Kant's "Copernican Revolution" in metaphysics changed the focus of metaphysical inquiry from nature exclusively to the thinking self as it understands nature. He argued that there are concepts—Categories—and space and time—Forms of Sensible Intuition—by which one understands and experiences things. Because one cannot but think things under these Categories and Forms, they are a priori conditions of different kinds of thought and therefore form the basis for judgments of necessity. Kant described his view as "transcendental idealism" because, although the Categories and Forms make possible objectively valid and necessary laws governing objects of experience, they cannot be ascribed to objects except insofar as those objects are experienced.

In experience, Kant rescued the traditional metaphysical distinction between form and matter: form is the a priori aspect of experience that mind imposes on matter in cognition. The inquiry into the nature of objects independent of experience by means of concepts, however, which Kant understood as the project of traditional metaphysics, cannot produce knowledge. However, Kant allowed that such inquiry, which he called "dialectic," is founded upon important human interests, such as the quest to understand practical freedom or to find purposiveness or systematic unity in nature.

Georg Hegel (1770–1831) held that ultimately only spirit is real. Hegel argued that history, in particular the history of human society, is a history of dialectical thought. Hegel, then, moved mind out of the individual altogether and eventually into an account of stages of human consciousness that are at once a kind of progression of reasoning, steps of psychological development, and social structures. Dialectic had a very different meaning for Hegel from that which Kant gave it. Hegel retained a focus on the process of reasoning that characterized Kant's dialectic and continued to consider the question of the invalidity of particular applications of a concept. The invalidity of a particular kind of reasoning is, however, of interest principally not because it makes a category mistake in applying concepts inappropriately but as itself a flawed way of being or experiencing objects in the world, which, because of its flaws, leads also to a particular new way of being.