 His most intrinsically important achievement arguably instead lies in his development of the thesis already mentioned earlier—contradicting such Enlightenment philosopher-historians as Hume and Voltaire—that there exist radical mental differences between different historical periods (and cultures), that people’s concepts, beliefs, values, sensations, and so on differ in deep ways from one period (or culture) to another. This thesis is already prominent in On the Change of Taste (1766) and it endures throughout Herder’s career (albeit with some periods of doubt or ambivalence). It had an enormous influence on successors such as the Schlegel brothers, Schleiermacher, Hegel, Nietzsche, and Dilthey.