In 1942, nearly a decade after Dirac's work, Richard Feynman built a new quantum mechanics formulation on the action principle. Feynman interpreted Dirac's formula as a physical recipe for the probability amplitude contributions from every possible path between x 1 , t 2 and x 2 , t 2 . These possibilities interfere ; constructive interference gives the paths with the most amplitude. In the classical limit with large values of action compared to h , the single classical path given by the action principle results.