This paper compares the claims about our knowledge of the external world presented by Rudolf Carnap, in the book known as the Aufbau, to those of Clarence Irving Lewis, in Mind and the World-Order. This comparison is made in terms of the opposition to Kantian epistemology that both books establish; the Aufbau is regarded as the peak of the logicist tradition and Mind and the World-Order is taken in continuity with pragmatism. It is found that both books present knowledge of (...) the external world as a consequence of a structural organization of human experience. However, there is an important point of divergence: the concept of verification each author adopts is different, such a concept was even a matter of discussion between Lewis and the Vienna Circle. This paper shows this disagreement but also shows how Carnap changed his point of view in the decade after the Aufbau was published, towards a standpoint which is much closer to Lewis’s ideas. In that process, nevertheless, Carnap changed his focus and did not deal with the problem of the external world anymore. This paper also seeks to draw attention to some features of the relation between Carnap and the pragmatist tradition which have only recently started to attract interest. (shrink)