This is a short preview of the full episode.
On Rudolph Carnap's The Logical Structure of the World (1928).
What can we know? Carnap thinks that all the various spheres of knowledge (e.g. particle physics, attributions of mental states, moral claims, the economy) are logically interrelated, that you can in fact translate sentences about any of these into sentences about sets of basic, momentary experiences. This book, better known as the Aufbau, is Carnap's attempt to sketch out how this system of linguistic reduction can work. Though it certainly doesn't work, it's a pretty damned fascinating attempt.
Carnap's hope was to integrate the language of scientific discourse with that of mathematics, and in doing so clarify traditional philosophical problems, in part by showing that anything that can't be recast in this philosophically respectable symbolic language is a bunch of vague nonsense. So we can describe the relations between the various contents of our experience, but the question of what these entities really are (i.e. the traditional realism vs. idealism debate) doesn't and can't arise in the system. Carnap at some points described himself neutral about such questions, but at others as hostile towards the dead-end sort of philosophy that generated them.
Matt Teichman rejoins Mark, Wes, and Dylan to get into some of the details of this very funky constructional system and try to figure out what good it is and whether one can really ignore such metaphysical questions when doing science. Read Mark's spiffy essay summarizing the topic and get the text.