Allowing for virtual paths in phase space permits an extension of Hami
lton's principle of least action, of lagrangians and of hamiltonians t
o phase space. A subsequent canonical quantization, then, provides a f
ramework for quantum statistical mechanics. The classical statistical
mechanics and the conventional quantum mechanics emerge as special cas
e of this formalism. Von Neumann's density matrix may be inferred from
it. Wigner's functions and their evolution equation may also be obtai
ned by a unitary transformation.