This study challenges the current view that the originality of Duns Scotus notion of contingent causality lies in modal logic. It works as an ontological concept, and so provides a point of entry into the foundations of Duns Scotus metaphysics.As one of two basic manifestations of the active causal power of being, it points to Scotus underlying ontology, which can no longer be seen as a failure to attain Aquinas clarity. We have a positive alternative, capable of generating the characteristic Scotist theses: univocity of being, formal distinction, haecceitas, proof of Gods existence from possibility, the producibility of Gods ideas.The exploration of the role contingent causality plays in Scotus and Bradwardines views on free will and predestination, and Bradwardines claim that God can undo the past, opens the way towards new interpretations.