Significance of Ehrenfest theorem in quantum-classical relationship

The significance of Ehrenfest theorem in quantum-classical relationship is discussed in terms of the general formulation of the theorem. With the ense mble interpretation of the quantum mechanical psi -function, the Generalize d Ehrenfest Theorem reveals some interesting exact relationships between qu antum and classical expectation values, These general results seem to imply a deep-rooted unity (in spite of apparent radical differences in conceptua l structures) between classical and quantum mechanics. Some significant con sequences and important physical insights which follow from the general for mulation are discussed with examples, Most important is that it offers, und er reasonable approximations, a pure quantum mechanical description of the Stern-Gerlach experiment with realistic inhomogeneous magnetic field (del . B = 0).