Open Theism (OT) is the view that God does not know in advance what people will freely choose to do in the future. One of the reasons some find OT attractive is that it offers a potential solution to the problem of why, if God knew the evil that this world would contain, He didn't create some other world instead that had less evil. That is, there must be an indefinite number of possible worlds God could have created, some of which would contain less evil than this one. If God knows everything that will transpire in any world He creates and if He is perfectly good then He would be expected to create the least evil world it would be possible for Him to have created, so either this world is the least evil world possible, which seems hard to believe, or God is not perfectly good, or God does not know in advance the free choices that people will make.
OT has been advanced by some philosophers as the least objectionable way out of the problem (See here for more discussion on Open Theism).
Alexander Pruss, however, doesn't buy it and offers an objection to OT at Prosblogion. Here's his criticism:
It seems to me that some folks--perhaps not philosophers--think that Open Theism (OT) somehow significantly helps with the Problem of Evil. But I do not think it does. The natural reason to think OT helps is to say that if an omnipotent God foreknows that George will freely do some evil E, then God can prevent George from doing E, and OT means that God can't foreknow it, so we can't blame God for failing to prevent E. But this is confused. For it would be impossible for God to both foreknow--or even forebelieve--E and prevent E. Foreknowledge does let God put plans for an event into effect before the event happens, but for actual prevention of foreknown evils, what would be needed is Middle Knowledge, not foreknowledge.
In other words, God could have foreknowledge of the evil that would exist in this world and prevent it by not creating this world. So why did He create this world when He could have created another in which people were free to choose but more often, or even always, chose to do right? The open theist argues that in fact, the traditional view of omniscience is wrong. God doesn't know what choices free beings would make in whatever world God placed them in, and therefore, He didn't know that man would sin in this world. He knew it was possible, He knew what His response would be if man did sin, but He didn't, the open theist claims, know that it would actually come to pass that man would fall.
God created, in this view, the best possible world He could create for Man and placed Man in it with the freedom to requite God's love or reject it. When Adam underwent the temptation in the Garden all of heaven held its breath because the outcome was uncertain and when Adam succumbed all of heaven and earth was devastated by his failure. In this view, the world's evil is entirely Man's responsibility. God could have prevented it only by either not creating a world or not creating mankind with libertarian freedom. Both alternatives would have defeated the whole purpose of creating Man in the first place which was to have beings with which He could live in a significant love relationship.
At any rate, OT is not without its problems, but I don't think Pruss's concern is one of them.RLC