Scotus's Argument for Just One Self-Existent Being
What follows is the executive summary for why Scotus believes there can be just one self-existent being, which assumes a self-existent being has been proven from prior argument. For those wanting to better understand Scotus’s natural theology, I commend Thomas’s Ward’s recent book Ordered by Love.
If there were two self-existent beings, they would each have the property of self-existence in common. From there, we can say each either would or would not depend upon the property of self-existence.
However, if each depended on the property of self-existence, then we have the contradiction of a dependent-independent being. Alternatively, if they did not depend upon the property of self-existence, then the property of self-existence is insufficient to make something self-existent, which is contradictory as well.
In other words, by supposing there is more than one self-existent being, we encounter contradictory implications. Prior argument, however, has demonstrated that there is (at least one) self-sufficient being. So, what’s the solution?
Scotus tells us: whatever nature is self-existent cannot have (let alone share) the property of self-existence but must be self-existence and by implication is non-multipliable. It must be such that its essence is identical to its existence. That was Aquinas’s insight as well.