[Revised entry by Paul Guyer and Rolf-Peter Horstmann on May 5, 2026.
Changes to: Main text, Bibliography]
This entry discusses philosophical idealism as a movement chiefly in the eighteenth and nineteenth centuries, although anticipated by certain aspects of seventeenth century philosophy and continuing into the twentieth century. It revises the standard distinction between epistemological idealism, the view that the contents of human knowledge are ineluctably determined by the structure of human thought, and ontological idealism, the view that epistemological idealism delivers truth because reality itself is a form of thought…

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