If accepted, Hume's fork makes it pointless to try to prove the existence of God (for example) as a matter of fact. If God is not literally made up of physical matter, and does not have an observable effect on the world virtually all theists believe that God has an observable effect on the world since they believe it is his creation, making a statement about God is not a matter of fact. Therefore, a statement about God must be a relation of ideas. In this case if we prove the statement "God exists," it doesn't really tell us anything about the world; it is just playing with words. It is easy to see how Hume's fork voids the causal argument and the ontological argument for the existence of a non-observable God. However, this does not mean that the validity of Hume's fork would imply that God definitely does not exist, only that it would imply that the existence of God cannot be proven as a matter of fact without worldly evidence.