As the deadline for raising the government debt limit fast approaches, and wrangling on the issue in Congress intensifies, Mariana Mazzucato reminds us of the difference between public and private debt. Professor of economics at the University of Sussex, Mazzucato is the author of "The Entrepreneurial State: Debunking Private vs. Public Sector Myths." Her provocative "they-didn't-build-that" thesis, that the government funds most of the initial research and development on which the private sector capitalizes, has generated a lot of buzz in the financial press, including Martin Wolf's review in the Financial Times calling it "basically right." So we asked her to explain her thinking to our Business Desk audience.