  The usual formulation of quantum theory is rather abstract. In recent work I
have shown that we can, nevertheless, obtain quantum theory from five
reasonable axioms. Four of these axioms are obviously consistent with both
classical probability theory and quantum theory. The remaining axiom requires
that there exists a continuous reversible transformation between any two pure
states. The requirement of continuity rules out classical probability theory.
In this paper I will summarize the main points of this new approach. I will
leave out the details of the proof that these axioms are equivalent to the
usual formulation of quantum theory (for these see quant-ph/0101012).
