Karl Fortlage (12 June 1806 – 8 November 1881) was a German philosopher. Born in Osnabrück, he taught in Heidelberg and Berlin before becoming professor of philosophy at Jena in 1846, a post he held until his death. Originally a follower of Hegel, he turned to Fichte and the psychologist Friedrich Eduard Beneke, agreeing with his assertion that psychology is the basis of all philosophy. The fundamental idea of his psychology is impulse, which combines representation (thereby presupposing consciousness) and feeling (i.e. pleasure). Reason is the highest thing in nature, i.e. it is divine in its nature. God is the absolute Ego, and the empirical egos are his instruments.