* This is, in fact, my third attempt to explain and defend the thesis. In the first German version (Spohn 1997) the thesis was embedded in a number of general observations about epistemology. This attempt was reduced to its core in the second English version (Spohn 1998). The present version is updated in various respects and will put the emphasis on what I call the third argument (in section 5) that I had in mind from the beginning, but recognized only after the second version as being in the center of the dispute.