In this two-page paper Puccetti presents a self-confident challenge to the concept of omniscience. Suppose that X fully knows Y, “the totality of facts constituting the world.” (God knows all the possible or rather ideal worlds, too.)

For in order to know he is omniscient, X would have to be certain there are no facts beyond those he knows. Thus, he needs to know something besides Y.

He needs to know the truth of the negative existential statement: (Z) “There are no facts unknown to me.”

Puccetti finds this problematic:

Yet X can only arrive at the limit of the known. It makes no sense to imagine X arriving at this limit, peering beyond it (at what?), and satisfying himself no further facts exist.

So long as he, like us, can conceive there being facts still unknown it will never be contradictory to deny he knows Z.

For the same reason our hypothetical X can never ascertain his own omniscience. (379-80)

Now first of all, it may simply be true that God is omniscient. If Z is true, and God believes it, then these may be enough to ascribe omniscience to Him.

The issue our author raises then is rather how God can be justified in believing Z. What are His reasons for holding it to be true? What is God’s evidence for His own omniscience? In other words, God must be justified in (correctly) believing that

  1. He knows everything about Himself;
  2. He knows everything about the created world;
  3. there is nothing else to be known.

Regarding (1), we can invoke the doctrine of divine simplicity. God is His own knowledge of Himself. God’s act of understanding is God; therefore, there is no aspect of Him (or an aspect of the world, for that matter, because God’s effects pre-exist in Him as in the first cause), of the existence and properties of which God is not aware.

In other words, the act of God’s intellect, understood as grasp of His natural (as distinct from middle and free) knowledge, is His substance; it subsists in itself; God is a “thought thinking itself.”

Hence God’s evidence for the true belief that He knows everything about Himself is His knowledge that He is simple and that His act of understanding is His own essence. In God there is no distinction between the subject knowing, the object known, and the intelligible species representing, and God is aware of that. God comprehends Himself 100%.

It may, of course, be asked again, how God is justified in knowing these things. The answer is that if you think that you are composite, then you are composite. This is because, if God believes Himself to be composite, then there are in His mind at least two parts of which He is made up (e.g., substance and accident, or essence and existence). But God’s knowledge is His substance. Whatever He knows, He is. Hence God would be composite, contrary to what is true. In other words, God has no choice but to think of Himself (truly) as simple, and His inability to think otherwise is His evidence for His simplicity.

Regarding (2), God can be sure that He knows the created world because God is “being itself subsisting” and the source of all being. His knowledge, when united with an act of will and an exercise of power, is the cause of all that exists; therefore He knows all that exists (through Himself). God cannot “miss” anything, because if something is out there, then it must have been He who brought it into being by giving it a gift of His own essence/existence. Having done this, He counts even the hairs on His creatures’ heads.

Regarding (3), again it may be asked how God knows that He is the sole creator of all things. This pertains to the question of the unity of God: are there or can there be multiple Gods? Well, perhaps God can reason like St. Thomas does in (ST, I, 11, 3) or (SCG, I, 42) to assure Himself that He is the one and only God.


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