On Russell's Introduction to Mathematical Philosophy (1919), ch. 1-3 and 13-18.
How do mathematical concepts like number relate to the real world? Russell wants to derive math from logic, and identifies a number as a set of similar sets of objects, e.g. "3" just IS the set of all trios. Hilarity then ensues.
This book is a shortened and much easier to read version of Russell and Whitehead's much more famous Principia Mathematica, and given that we can't exactly walk through the specific steps of lots of proofs on a purely audio podcast (nor would we want to put you through that), we spend some of the discussion comparing analytic (with its tendency to over-logicize) and continental (with its tendency towards obscurity) philosophy.
Running Time: 1 hr., 31 min. Recorded: April 24, 2011. Participants: Mark, Wes, and Josh Pelton
As a bonus, your purchase includes a high-bitrate mp3 of the song that concludes the episode, “Words & Numbers,” by Mark Lint & the Madison Lint Ensemble(2004, completed 2011).