Illustration of a philosopher delivering a speech on Kantian ethics and philosophy to a sleeping audience in 19th century society. A portrait of Immanuel Kant (1724-1804) is depicted on the wall. In his doctrine of transcendental idealism, Kant argued that our perception of the world is not simply a passive reflection of reality, but rather an active construction that is shaped by our mental faculties. Therefore, the nature of things as they are in themselves is unknowable to us. Print by Jacob Ernst Marcus after design by Christiaan Josi circa 1800-1805.