Why must we work in the phase space?
  We are going to prove that the phase-space description is fundamental both in the classical and quantum physics. It is shown that many problems in statistical mechanics, quantum mechanics, quasi-classical theory and in the theory of integrable systems may be well-formulated only in the phase-space language. 
J. J. S{\l}awianowski, F. E. Schroeck, Jr., A. Martens
math-ph math.MP