 First, according to the view known as “open theism,” God cannot know those parts of the future that are yet to be determined, such as the future free actions of human beings, either because there are no truths to be known yet or because there is no way for anyone, including God, to know them (see Hasker 1989, Rissler 2006, the entry on  process theism,  Other Internet Resources). This does not mean the God is not omniscient, because God still knows everything that can be known (and that is what it means to be omniscient, according to open theists). So open theists have a way to defuse the puzzle for petitionary prayer involving omniscience concerning the future: if our prayers are free, or God’s decision whether or not to answer them is free (or both), then those things cannot be part of a determined future and God cannot know about them in advance. But open theism is controversial because (among other things: see Rissler 2006) it appears to deny something that theists have affirmed traditionally, namely, that God knows the future in all of its detail.