Die Sprachen sind nicht nach dem logischen Lineal gemacht. (Briefwechsel, p. 102) If success in solving problems is the hallmark of philosophical great­ ness, then Frege was not a great philosopher. But by that same token, very few if any other figure in the history of philosophy will qualify. On the other hand, if the hallmark of philosophical great­ ness is the opening up of new conceptual territory and the raising of hitherto unsuspected crucial questions, the shifting of philosophical perspectiv~ and the determination of subsequent lines of enquiry, then Frege must rank among the greatest philosophers of all times. He was the first to develop a completely formalized language and a logical system sufficiently powerful to generate arithmetic; he opened up the fields of philosophy of logic and arithmetic; his theses on sense reference and definition were seminal to almost all subse­ quent work done in the philosophy oflanguage; and his ontological speculations constituted the foundation of one of the most profound metaphysics ever developed: that of Ludwig Wittgenstein in the Tractatus.