One of the things I’ve been observing during my interactions with presuppositionalists is that at least some of them seem to have a strange view of what “necessary” means. The presuppositional argument declares that there are two types of entities: necessary things and contingent things. A contingent thing depends on something else for its existence and characteristics, whereas a necessary thing exists because it must necessarily be real. There follows a certain amount of philosophical discussion (and/or hand-waving, and/or smoke and mirrors) gradually working its way to the conclusion that everything depends on God being real, and therefore God must be real. And not just any God, but a specifically Christian, Trinitarian God to boot.
The obvious flaw in this argument is that, even if we accept the existence of a necessary being, there’s no reason why it should have to be any sort of god, or even any sort of person. God might arguably be a conceptually possible being, but if He’s only a possible being, then by definition He’s not the necessary being. Yet presuppositionalists (or at least some of them) clearly believe that God is not just a possible being, but a literally necessary one. And I think I might have some understanding as to why and how they think that.