Hi. Is the principle of least (better: stationary) action only an axiom in classical mechanics, or can it be derived from a more profound (classical) principle? As far as I know, it can be derived from the path integral formulation of QM. Is this a more profound justification for the principle of least action? Or are we just moving in circles, since QM emerges from canonical quantization of a classical Hamiltonian where the principle of least action has already been used? If QM is indeed a more profound justification of the principle of least action, does this imply that QM might be necessary for classical physics?