It is usually assumed that the modal ontological argument is valid. However, the logical system in which the argument is analyzed can require different assumptions to secure validity. Some strategies for the both critics and proponents of the modal ontological argument are examined in different logical systems. For agnostics, statements involving a perfect being may have a truth value other than true or false. A many-valued modal logic may be a more suitable framework for agnostics, and the modal ontological argument will be invalid in some many-valued modal logics. These considerations show that defenders of the modal ontological argument must also defend the choice of a particular logic (or class of logics) as the appropriate setting where the argument should be evaluated.