 By the time of the book’s publication the emphasis had shifted, but the idea of bringing all concepts into a single deductive system survives. In a popular lecture given in Vienna in 1929, Carnap explains the point of his book by telling a dialectical story of human history as a struggle between “critical intellect” and “imagination”. At first imagination ruled the day, but then in antiquity, critical intellect made a discovery that enabled it to put strict limits on imagination’s claims: 