According to most Anselmians–and most theists–God has a special set of essential properties. Those essential properties include omniscience, omnipotence, perfect goodness and necessary existence. But how do we know this? There are just two possibilities: either we know that God has those essential properties apriori or we know aposteriori. Again, almost no theist maintains that we know the essential properties of God aposteriori. The reason this is rejected is because it entails that we might have discovered that God was less than essentially perfectly good, etc. But almost no theist thinks that’s a possible discovery. So, most Anselmians–I’d again say most theists–maintain that (A) is true.
A. A being x = God only if (i) for most essential properties P of x, it is
primarily necessary (i.e., apriori) that x has P, and (ii) the essential properties of x
include omnipotence, omniscience, perfect goodness, and necessary existence
There is a concise and valid apriori demonstration based on (A) and some well-known logical relations holding between primary necessity (aprioricity) and secondary necessity (metaphysical necessity). Let M be restricted to essential properties understood as properties objects have in every world in which they exist. Here’s a concise ontological argument.
1.0. â¡1âx(â¡1Mx â â¡2Mx)
(1.0) states that, it is apriori that x instantiates essential property M, only if it is metaphysically necessary that x instantiates essential property M. For instance, if it is apriori true that the empty set instantiates the essential property of being non-membered, then it is metaphysically necessary that the empty set instantiates the essential property of being non-membered. Now instantiate (1.0).
1.1. â¡1(â¡1MG â â¡2MG)
(1.1) says that If it is apriori that God has essential property M, then it is metaphysically necessary that God essential property M. But we know from (A) that (1.2) is true.
It is an apriori known conceptual truth, based on (A), that God has the essential properties of omniscience, omnipotence, perfect goodness and necessary existence. But then, obviously, (1.3).
It is metaphysically necessary that God has the essential properties of omniscience, omnipotence, perfect goodness and necessary existence.
The argument is valid. And it makes no mistakes in moving from conceivability to necessity. The principle in (1.0) properly licenses that inference. And it would be sound if (A) were true. But I’m not sure (A) is true. Is it an apriori knowable conceptual truth that God instantiates the divine essential properties? Norman Malcolm thought so, and so did Anselm of Proslogion 3. Suppose it isn’t apriori knowable. Then it can be no more than aposteriori knowable that God instantiates the divine essential properties. That’s a pretty startling conclusion that is contrary to what most theists and certainly most Anselmians believe. It entails that we might have discovered that God had quite a different set of properties.