Someone asked how God can know there are this-many hairs on my head at one point and then this-many hairs on my head at another point without God changing essentially.
Here is how God can know these things while still being immutable. However, we must take the answer in steps.
First, we must recognize that God does not know contingent things the way we do: that is, by encountering them as already existing. God knows contingent things by causing them to exist. So, the directionality is different. Whereas contingent things cause knowledge in us, it is God’s knowledge that causes contingent things. In other words, God knows how many hairs are on your head by making it to be the case that you have (x) number of hairs on your head.
Second, God is eternal. So, God can will, in all eternity, that you have (x) number of hairs from t1 to t7 and then a different hair count from t7 t7 to t9; thus, your hair count can change over time without God changing in His eternity. (Even more, God can will – again, in all eternity — to give you more hair at t7 because of your praying for more hair at t5. This is pointed out simply to rebut the erroneous assumption that God being eternal implies can cannot be responsive.)
Third, God’s causal act of creating you with (x) number of hairs is extrinsic to God. Why so? Because God’s causal act of creating you with (x) number of hairs just is you existing with (x) number of hairs (based on God’s exemplar knowledge) with your causal dependence relation on God. There is no change in God when this occurs because the action of the agent is entirely IN THE PATIENT. Further, God’s action is basic and immediate and does not run through intermediary channels (such as God forming some prior intrinsic intention). So, when God causes anything God directly and immediately brings that thing into existence, and God does so based on reasons which God knows in his self-understanding (again, all in one simple and eternal act of self-understanding), and so God’s causal act is truly intentional and cognitional, hence it makes sense to say that God “decided” or God “intended” or God “chose” for you to have (x) number of hairs on your head. As such, when we say that God knows you with (x) number of hairs on your head, this is an extrinsic predication, and because divine simplicity claims only that all God’s intrinsic properties are identical with God, and because God’s causing and therefore knowing you with (x) number of hairs on your head is extrinsically denominated (that is, grounded in something extrinsic to God: namely, YOU with your causal-dependence relation on God), that can change without any real or essential change IN God. Thus, divine simplicity and immutability is preserved alongside a contingent, changing creation.
As Matthews Grant explains, “If God knows contingent objects in the act of intentionally bringing them about and if, as EM maintains, God’s intentionally bringing an entity about does not involve anything intrinsic to God that would not exist were God not bringing that entity about, then God can know contingent objects without there being any intrinsic accidents in God.” (Source: Free Will and God’s Universal Causality.)
One final word on this, this time about human freedom. Because it is often claimed that God’s omniscience or foreknowledge is incompatible with human libertarian freedom. If God knows what I am going to do 5 minutes from now, then I must do what God knows I am going to do 5 minutes from now. How, then, am I substantially free?
There are many problems with this objection but let’s begin with the most basic. First, it is a fallacy to assume that just because someone knows what you are going to do you aren’t doing it freely. Imagine a person peering into a crystal ball, looking into the future. They see you freely eating a hamburger and know with certainly (assuming the crystal ball is reliable) that is going to happen. Does this negate the fact that you have freedom or won’t eat the hamburger intentionally and voluntarily? If so, it is hard to see how; the objection is (at best) underdeveloped. However, the point of this illustration is simply this: Knowing that something will happen in the future – in fact, even if you necessarily know that something will happen in the future – it does not follow that necessarily that something had to happen. It could have been otherwise.
More specifically, that God necessarily knows you will do (x) only means that you will in fact do (x), not that necessarily you had to do (x). For it could have been otherwise, and, in which case, God would have known otherwise. The point is this. The move from God necessarily knowing something to necessarily that something happening is a modal fallacy.
But the confusion is even worse than that. Because, technically speaking, God doesn’t have “foreknowledge” to begin with. God’s knowledge is eternal, with all points in time simultaneously present before Him, as we’ve already discussed. So, when God knows what you are doing, it is less like looking into a crystal ball and more like you acting right in front of Him. And surely my knowing that my wife is sitting HERE AND NOW (which I know by sitting across from her and immediately seeing what she is doing) clearly entails that she is sitting HERE AND NOW. But that is just reiterating the principle of identity: if my wife is sitting, then my wife is sitting. And there is nothing remarkable about that. Thus, it doesn’t follow that my wife had to be sitting. She could have been standing. So, if there is no incompatibility with our knowing something in the present and that something being contingent or free, then what is the problem with God knowing something as present in all eternity and that something being contingent or free?
But perhaps the attentive reader will note that God isn’t just watching us sit, he is causing us to sit, and there he is correct. God IS causing us to sit. The assumption, however, is that God cannot cause freely creaturely actions, and that assumption is false. God’s causality is transcendent and indeed the source of all contingent being, including free creaturely being. God knows our actions in bringing them about, but God’s action is concurrent with our action qua rational agents (makes our concurrent action possible, in fact), which gives us counterfactual power over God’s causing and knowing. If we had down otherwise, God would have caused and known otherwise, and this is no threat to divine immutability or simplicity because, as already stated, the predication is extrinsic, merely Cambridge. But still, God has counterfactual power over us, as well. For what it’s worth, this is known as the Dual Sources account, developed by W. Matthews Grant, and for a detailed defense I (yet again) gesture in the direction of his book. But what’s been said up to this point should be enough to see through condescending dismals and underdeveloped objections aimed at God’s knowledge, human freedom, and divine simplicity.
Related Resources
Feser has a good analogy on God’s causality and human freedom, as well.