ABOUT BOOK

I present a selection of conceptual and mathematical problems in the foundations of modern physics as they derive from the title question. Contribution to a panel session, "Springer Forum: Quantum Structures -- Physical, Mathematical and Epistemological Problems", held at the Biannual Symposium of the International Quantum Structures Association, Liptovsky Jan, September 1998. To appear in journal: Soft Computing (2001).Comment: 3 pages, tcilate