Just One Necessary Being (Part 2)

Building upon a previous post:

Imagine two necessary beings. For these being to not be the self-same reality, there must be some difference between them: some additional feature, as it were, atop their necessary nature which they have in common. However, if the difference is contingent, then the being is composite and requires a cause, contradicting its necessary nature. Alternatively, if the differences are necessary to each, then each lacks some essential feature that some other thing has on account of having a necessary nature, and so is not necessary and we encounter another contradiction. We are thus constrained in the number of necessary realities – if there is any necessary reality at all – being just one.

Or consider the matter this way:

Say there is an individual necessary existent (NE).

Either NE is individuated through itself or through another. However, if NE is individuated through itself (that is, its essence) then every necessary existent having the same essence as NE is identical to NE. In which case, there can be just one necessary being.

Otherwise, if NE is individuated through another, then NE must be caused in some respect. But NE is entirely uncaused. So, NE cannot be individuated through another.

There is — and can only be — just one NE.

Consider also:

Suppose two individual instances of subsistent existence: NE1 and NE2, each identical to its existence and therefore a necessary being.

However, if these realities are distinct, then the existence of NE1 is distinct from the existence of NE2. In which case the existence of each one is individuated by that of which it is the existence: the existence of NE1 is individuated by NE1 and the existence of NE2 is individuated by NE2. Hence each one is distinct form its existence. But each one is by hypothesis the same as its existence. Thus, there can be just one subsistent existence (necessary being).

Summary: Given Aquinas’s essence-existence metaphysics, if there is a necessary being, then it must be “uniquely unique.” For there could be nothing that shared Y’s essence and that was identical to Y’s existence without being identical to Y.