The argument from incoherence is a sound argument for the non-existence of God.

I wish to thank Microsuck for the challenge, and am pleased to be debating him again.It seems self-evident that things with contradictory properties cannot exist. However, there are some properties that seem contradictory which, when you really examine them, are not contradictory at all. Take Pro's example of the invisible pink unicorn. However, it is not contradictory for an invisible entity to be pink or a unicorn (unless I am misunderstanding the analogy). Take Klingon Birds-of-Prey, from Star Trek lore. They are starships that can render themselves invisible to avoid enemy detection. However, once invisible they no longer cease to be starships, and they no longer cease to be green. Once they "de-cloak" (that is, become visible), they are the same green starships that they were before they cloaked. Simply because you can't see something visibly does not mean it doesn't have attributes which you could notice if you could see the entity.I agree that entities that are logically incoherent, such as square circles or married bachelors, cannot exist. The question remains, is God logically incoherent? I will attack Pro's second premise.Premise 2 -- God has incoherent attributesOmniscient vs. OmnipotentIt is true that God is all-knowing and all-powerful. These are great making properties and God, as a maximally great being, has all great making properties (that is, properties that are better to have than not to have), and has them to their maximal extent.It is true that God knows the future. It is also true that God can change the future, if he wishes. This is not contradictory. This is because God knows all possible futures. For example, take the case of Jonah and the Ninevites. Jonah was instructed by God to go to Ninevah to encourage them to repent of their sins, for they were going to be destroyed due to their wickedness in forty days (Jonah 3:4). God knew this was going to happen, and left alone this would have happened. However, God is also a merciful God. Jonah (eventually) preached to the people of Ninevah, and they repented of their wickedness. Therefore, God had mercy on them and did not destroy them. God knew that He was going to destroy the city if they did not repent, but God being a merciful God spared their city because of their repentance. This can also be seen in the ultimate destination of all mankind. Everyone is on their way to Hell, but they can change their destination if they repent and trust in Jesus for their salvation. God doesn't just know the future, He knows all possible futures.Now, there are some things that can't change. God knew that He was going to create mankind, that humans would sin, and he would eventually have to send Jesus to save us from their sins. These were decreed by God and could not be changed.Regarding Pro's analogy, there are ways we could change the election. If you hated Obama and knew he was going to win the election, you could assassinate Obama. Therefore, he would not be alive to take office (and note, I am not advocating the assassination of our president). God does, indeed, have control over the future. But the future is not always set in stone. For example, the reason God has not returned yet (for his second coming) is because he is tarrying, wanting everyone possible to come to repentance so they can spend eternity with him (2 Peter 3:9).Free will vs. All-knowingIt is not impossible for an omniscient being to be free. Not only does God know what actions he will do, but he also knows what possible actions he would do under certain conditions (such as in the example of Jonah, above). Therefore, premise four in the argument fails. An omniscient being surely knows that actions could have several possible outcomes, and an omnipotent being would not necessarily have to be locked into a particular action, unless he has given his word that the particular action would occur.This also overlooks the simple fact that an omniscient being would know a particular action will occur, even though a less desirable action may occur. For example, even though God told Jonah he will destroy Ninevah in forty days (due to their wickedness), he definitely knew that they would repent and that he would spare them, before the events even occurred. So in that respect, he does know exactly what will happen even though there is the possibility of different outcomes.Simply knowing what actions will occur does not mean that God wasn't free to do otherwise. For example, God could have just as easily not created the universe. The fact that he knew ahead of time that he would created it does not mean he wasn't free to create it. It just meant he knew what he would do ahead of time. Just like if you know you're going to go to the mall next Saturday, you are still free to do otherwise. You could have any number of good reasons for not going, or you may just not feel like going that day. The difference is that God, being omniscient, knows for sure what will happen and it won't change (or if it will change, God knows that, too).Conclusion God does not have contradictory attributes. His existence is not in question, due to the fact that omnipotence paradoxes and trying to prove God has contradictory attributes simply do not work. God is a maximally-great being, so he has all great making properties to their maximal extent. If he didn't, he would not be God.