Avicenna’s proof for the existence of God (the Necessary Existent) in the Metaphysics of the Salvation relies on the claim that every possible existent shares a common cause. I argue that Avicenna has good reason to hold this claim given that he thinks that (1) every essentially ordered causal series originates in a first, common cause, and that (2) every possible existent belongs to an essentially ordered series. Showing Avicenna’s commitment to 1 and 2 also allows me to respond to Herbert Davidson’s and Richard Swinburne’s claim that Avicenna’s proof for the Necessary Existent is incomplete and fallacious.
