  We introduce a framework for studying non-locality and contextuality inspired
by the path integral formulation of quantum theory. We prove that the existence
of a strongly positive joint quantum measure -- the quantum analogue of a joint
probability measure -- on a set of experimental probabilities implies the
Navascues-Pironio-Acin (NPA) condition $Q^1$ and is implied by the stronger NPA
condition $Q^{1+AB}$. A related condition is shown to be equivalent to
$Q^{1+AB}$.
