  Is quantum mechanics about 'states'? Or is it basically another kind of
probability theory? It is argued that the elementary formalism of quantum
mechanics operates as a well-justified alternative to 'classical'
instantiations of a probability calculus. Its providing a general framework for
prediction accounts for its distinctive traits, which one should be careful not
to mistake for reflections of any strange ontology. The suggestion is also made
that quantum theory unwittingly emerged, in Schroedinger's formulation, as a
'lossy' by-product of a quantum-mechanical variant of the Hamilton-Jacobi
equation. As it turns out, the effectiveness of quantum theory qua predictive
algorithm makes up for the computational impracticability of that master
equation.
