These questions are glossed over although they are basic to any deep understanding
of the big ideas of geometry and the historical revolution whereby
mathematics went from being The Truth to an axiomatic system unrestrictedto traditional commonsense views of three-dimensional space. In light of the
need for rethinking and shifts of perspective, it is easy here to uncover some
of the vital inquiries the debate over the postulates spawned: Why do we
assume what we do? When should we change our assumptions and why? Flatland
(Abbott, 1884/1963), a fictional account of other spatial worlds, is a fascinating
and readable introduction to the issues, written more than a century
ago to serve just such a purpose.