If success in solving problems is the hallmark of philosophical greatness, 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 greatness is the opening up of new conceptual territory and the raising of hitherto unsuspected crucial questions, the shifting of philosophical perspective 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 subsequent work done in the philosophy of language; and his ontological speculations constituted the foundation of one of the most profound metaphysics ever developed: that of Ludwig Wittgenstein in the Tractatus.