Johann Nicolaus Tetens, the German philosopher and psychologist, was born in Tetenbüll, Schleswig, in 1736 or in Tönnig, Schleswig, in 1738, and died in 1807. He studied at the universities of Rostock and Copenhagen and became a Magister at Rostock University in 1759. From 1760 until 1765, when he became director of the local Gymnasium, he taught physics at Bützow Academy. He was full professor of philosophy at the University of Kiel from 1776 to 1789, during which period he also carried out an official study of the local hydraulic installations on the North Sea coast. From 1789 until his death he had a brilliant career as a high financial official in Copenhagen.

Tetens was strongly influenced by J. C. Eschenbach, his teacher of philosophy at Rostock. Eschenbach was an eclectic who accepted some Leibnizian and Wolffian tenets but sided with the Pietists against Christian Wolff...