It is now more than a year and a half since Professor Stegmüller kindly sent me a copy of his Theorie und Erfahrung (Stegmüller, 1973), thus drawing my attention for the first time to the existence of Dr. Sneed's new formalism and its likely relevance to my own work. At that time set theory was to me an unknown and altogether forbidding language, but I was quickly persuaded that I must somehow find time to acquire it. Even now I cannot claim entire success: I shall here sometimes refer to, but never attempt to speak, set theory. Nevertheless, I have learned enough to embrace with enthusiasm the two major conclusions of Stegmüller's book. First, though still at an early stage of its development, the new formalism makes important new territory accessible to analytic philosophy of science. Second, though sketched with a pen I can still scarcely hold, preliminary charts of the new terrain display remarkable resemblance to a map I had previously sketched from scattered travellers" reports brought back by itinerant historians of science.