Free Will Theism + Presentism = Open Theism
Suppose that free will theism is true.
Free will theism entails theism, the thesis that God exists, where 'God' is understood to denote a necessary being essentially possessing the greatest possible set of compossible great-making properties, including maximal power, knowledge, and goodness.
Free will theism also entails that God has created a world of creatures some of which are free in the 'libertarian' sense. Libertarian freedom is incompatible with determinism and thus implies that the future is 'causally open' with respect to creaturely free choices. In other words, there are 'future contingents'.
Suppose further that presentism is true. Presentism is the thesis that whatever exists, exists now, in the present.
Grant both of those theses (free will theism and presentism), along with two additional widely accepted notions - the correspondence theory of truth and the causal dependency of later states on earlier states - and one gets a straightforward argument for open theism, a species of free will theism that holds that the future is epistemically open for God in precisely those respects in which it is causally open.
Here's the argument:
- God’s knowledge corresponds to what is true. (divine omniscience)
- What is true corresponds to what is real. (correspondence theory of truth)
- God’s knowledge corresponds to what is real. (from 1 and 2)
- What is real corresponds to what is present. (presentism)
- God’s knowledge corresponds to what is present. (from 3 and 4)
- What is future stands to what is present as an effect does to its cause. (time order of causal dependency)
- The future is epistemically settled for God iff the future is fully ‘present in its causes’. (from 5 and 6)
- The future is not fully present in its causes. (future contingency)
- The future is not epistemically settled for God. (from 7 and 8)