  The same set of physically motivated axioms can be used to construct both the
classical ensemble Hamilton-Jacobi equation and Schrodingers equation. Crucial
roles are played by the assumptions of universality and simplicity (Occam's
Razor) which restrict the number and type of of arbitrary constants that appear
in the equations of motion. In this approach, non-relativistic quantum theory
is seen as the unique single parameter extension of the classical ensemble
dynamics. The method is contrasted with other related constructions in the
literature and some consequences of relaxing the axioms are also discussed: for
example, the appearance of nonlinear higher-derivative corrections possibly
related to gravity and spacetime fluctuations. Finally, some open research
problems within this approach are highlighted.
