Explaining contingent facts

I argue against a principle that is widely taken to govern metaphysical explanation. This is the principle that no necessary facts can, on their own, explain a contingent fact. I then show how this result makes available a response to a longstanding objection to the Principle of Sufficient Reason—the objection that the Principle of Sufficient Reason entails that the world could not have been otherwise (i.e. that all facts are necessary).