Postulate 3 God is Being Itself.
This postulate immediately puts God in a different ontological status compared with us. We are beings, but we are not being itself. That God has that special status is distilled from Judaism in the saying that God is “I Am” (Exodus 3:14), and, from Christianity, in similar statements by Jesus (John 8:58). This distillation has long been part of classical theism. God is Necessary in comparison to us mortals who are contingent. God can thus be the necessarily-existing original cause of any finite thing that comes into being. Before considering the consequences of this postulate, let us make sure we understand it in more detail:
Assertions that ‘God is X itself’
Assertions that ‘God is X itself’
Postulate 3 is the first in a series of claims that God is X itself. Here X is ‘being’, while other features (such as ‘love’, ‘life’ and ‘wisdom’) will be attributed later. Such assertions have important roles in theistic metaphysics, and these roles need to be defined explicitly.
Consider a generic assertion of the form “Object G is X itself”. It first implies that, if G exists, it has description X necessarily. It is then part of its nature that G does not merely have description X, but that it does so at all times and in all counterfactual circumstances originating at any time. This does not imply immutable or fixed existence, only that property X is attributed at all times. That is a minimal requirement for any kind of eternal existence, though the actual manner or form of existence could be variable or fluctuating as long as it is always present.
A second component is to state that such a G is not an X exactly like other objects which are Xs, but that G is still essentially involved in the way they are Xs. Here, for example, God is not a ‘being’ precisely like the rest of us are beings, yet (as being itself) God is intimately involved in the way we are beings. God is still a being and still exists but in a different way then we.
From the existence of X-itself, we may deduce that every instance of X is either
(a) identical to X-itself, orWe conclude that if an object with property X exists completely independently (or ‘in itself’), then it must be identical to X-itself, since (by construction) it cannot be dependent on anything apart from itself. The present case, with X=being and God as being itself, implies that any existing object is either identical to God or dependent on God. If anything exists at all, we could conclude that God exists, but we already postulated that in Postulate 1. What this postulate adds is that God exists eternally and necessarily.
(b) dependent on X-itself.
You may dispute these kinds of arguments. You could ask: since this stone is brown, does that mean that brownness-itself exists? Does redness-itself exist? Or evil-itself, since there are many things thought to be evil? And if redness-itself did not exist, why is being-itself treated differently in theism? Theists reply that our argument for X-itself existing is not valid for every X. The argument depends on Postulate 3 for X=being and on later postulates for other Xs. These Postulates are not logically necessary for every possible X.
Alternatively, you could argue that since this stone is a being, and since God is being itself, we should conclude that this stone is God. Theists do not deny the validity of an argument like this. They insist only that it proceeds if the stone is in fact being, itself. That is: the argument is only valid if stones exist independently, eternally and necessarily, since being itself is eternal and necessary. Theists agree that if atoms in the world exist eternally and immutably then they could be said to have or be being itself. In that case, on the basis of Postulate 3 at least, they could be identified with God. This is the sense in which the atomic materialist makes atoms into his God. But we will understand theism differently.
Adapted from chapter 8 of Starting Science From God.