During the last two decades, there has been a revival of interest in Rudolf Carnap. This has led to the revision of various stereotypes about him, e.g., of the view that his first major work, Der Logische Aufhau der Welt (1928), represents a crude form of positivism or the culmination of classical empiricisms. Careful historical studies of the Aufbau have, instead, brought to lights its neo-Kantian and Husserlian roots, thus leading to a much subtler, more complicated story about the book's origins and goals. Another result of recent scholarship has been a shift of focus from the early Aufhau to Carnap's middle and later writings. Thus, his Logische Syntax der Sprache (1934-/1937) has been rediscovered as a major contribution to the philosophy of mathematics and logic, and Carnap's writings from the 194-0s and 50s have come into focus as well. One result of the latter shift is a renewed interest in his notion of...