Within the limits of possible knowledge, epistemologically speaking, I am as certain as a person could reasonably be that Mormonism is not True. Assuming, arguendo, the truth of Christianity, I believe that Mormonism’s claims to truth cannot possibly be true because of fatal flaws in the fundamental Mormon teachings about the Great Apostasy and the Restoration. As the new “discussions” reflect, Apostasy and Restoration are Mormonism’s lynchpins: without a Great Apostasy there was no need for a Restoration, and without a Restoration, Mormonism’s self-justifying truth claims fall apart.
For the Apostasy-Restoration to have happened, the following must be true:
1. Priesthood authority must indeed work the way the Mormon Church claims it does. This actually means that, in fact, the concept of priesthood authority is actually the most fundamental Mormon doctrine, because Apostasy-Restoration presupposes the existence of a priesthood authority that functions the way Mormonism teaches. The thing is, there is almost no evidence from the apostolic era or before (i.e., from the Bible or other contemporary sources) that priesthood authority–if it exists at all–works like that. Mormon scriptures do not count, because for them to be acceptable, Mormonism must be true which means that priesthood must work the way Mormonism says it does (which is what we’re trying to decide in the first place). That is, unless Mormon scripture was somehow independently verifiable, which it most certainly is not.
2. Said priesthood must have been lost in the manner that Mormonism claims. This requires us to believe a claim of Mormonism at face value, which we have no reason to do unless we first accept that Mormonism’s concept of priesthood authority is true and that the Apostasy-Restoration actually happened. Again, if we could verify this loss of priesthood independently, Mormonism would be more credible. But we can’t. Change in doctrine does not evidence loss of priesthood authority, because that requires us to first accept a Mormon understanding of how priesthood works. Ditto for basically every other Mormon evidence of the loss of priesthood leading to the great apostasy. The Bible verses appealed to by Mormonism do not really help, either: taken alone, without presupposing Mormon priesthood authority, and Apostasy-Restoration, they do not by any means necessarily mean what Mormonism says they mean. The fact that the idea of a Great Apostasy was common in the 19th century is also not dispositive. Nobody thinks that anymore. A vague semi-consensus among some–but by no means all–Protestant Christians in the 1800s that something like the Great Apostasy had happened cannot possibly be credible evidence now that it actually did happen. Furthermore, Mormon claims about the loss of priesthood–and what would have had to have happened for such a loss to occur–are facially implausible. Even if we do accept Mormon ideas about priesthood authority and how it works, the likelihood that it would be lost while Christianity would survive is completely unbelievable. I wrote a post awhile back explaining exactly why. I think it is well worth the read.
So we have no reason to believe that priesthood works the way Mormonism says it does or that a Great Apostasy happened, except for circular logic that requires us to first assume the truth of Mormonism. That means Mormonism’s claims are simply not credible unless we believe Mormonism’s claims of authority based on nothing but… Mormonism’s claims to authority. Even the official Way To Truth (read, pray, feel-the-spirit-confirming-the-truth-and-banishing-all-doubt-and/or-contrary-evidence, rinse, repeat ad nauseum) requires us to begin by assuming that Mormonism is right regarding how you find out what is true. Unless you independently think that the Mormon Way To Truth is the right way to truth, or even one of several reliable ways, we have no reason to trust Mormonism when it tells us the way to truth, since it does it based on its own authority, which is what we’re trying to verify in the first place. This is textbook circular reasoning.
As far as independently thinking–i.e. based on something other than Mormonism’s teachings–that the Mormon Way To Truth is in fact the right way, I have a lot to say about that. But for the moment I will merely point out that no other religion or religious leader teaches it. If it was independently verifiable or somehow self-evident, the chances are pretty good that someone would actually have come up with it on their own (and then if Mormonism was really true, it would have to lead them to Mormonism). Good luck trying to argue that this in fact happens.