Circular Reasoning & The Bible
Every philosophy, epistemology, and theology has, at its root, some form of circular reasoning. It's just a matter of recognizing it. By asking "Why...why...why...?" enough times, one can eventually expose the source of nearly all of one's presuppositions. I bring this up, not to expose those who use circular reasoning as if they are at fault for doing so, but rather to help us evaluate the validity of our sources.
Consider the atheist...ask them why they don't believe in God, and you will get a variety of answers. Some cite reasons that sound more like they don't have a reason while others might have had a painful life experience that caused them to not only question God, but to reject their belief in Him altogether. The former assumes that God does not exist based on no other basis of belief except what they think for themselves. This is a faulty presupposition, however, because everyone will admit that they are not perfect and that they have made wrong assumptions and decisions in the past. Why, then, should they, I, or anyone for that matter, trust in themselves as the source of definitive knowledge regarding an issue as important as the existence of God?
In the latter case, on the other hand—not to downplay the extent to which such horrific life experiences can destroy a person's confidence and purpose—they base their rejection of God on the fact that they believe God, if He even exists, should be different than they were expecting. Perhaps they believe God should be more willing to let them keep the job they lost, or keep their legs after an accident, or keep their spouse that passed away. These are crippling life experiences for sure, but are these the things that would make God good? Why would we begin to presume such things based only on our own notions, which we have acknowledged up to this point to be faulty more often than we would really like to admit? Holding to an idea for no other reason than because they simply believe it, is faulty logic, NOT because it is circular reasoning, but instead because they are not always right, so there is no reason to definitively believe that they are right in this case.
On the other hand, for the Bible-believing Christian, when asked why they believe in God, says...
"Because the Bible says that God exists."
Why should I believe the bible?
"Because the Bible is true."
How do you know it's true?
"Because the Bible says the Bible is true."
This is not faulty reasoning even though it does involve circular reasoning. It is only faulty if someone can point out an irreconcilable error in the Bible. By "error," I mean to refer only to blatant contradictions or facts that can be incontrovertibly disproved, and I do not believe there are any (cf., 2 Timothy 3:16). "Mysteries," however, are not uncommon in scripture, but just because we can't explain something does not require us to abandon it—because our knowledge is subject to God, not the other way around. Now, the believer will naturally strive to defend scripture as they are confronted with issues that challenge it, but this is not to lead anyone to conclude that the only way to believe the Bible is true is if they first successfully extinguish every issue ever raised against it. On the other side of the coin, the non-believer will likewise naturally strive to disprove scripture. But the non-believer's presuppositions are faulty for the reasons explained above, whereas those of the believer are not.
Logically, one does not need a reason to believe that something is true, but having a reason why it is not true requires one to abandon that belief. That being said, suffice it to say I still think there are a number of reasons to believe that the Bible can be trusted as true, which include, but are not limited to, the following: it is full of hundreds of prophecies regarding the life and death of Christ that were accurately fulfilled (cf., 2 Peter 1:20-21), and it is extremely accurate both historically and scientifically.
But what about the Bible's authors, one might ask? Aren't they just as fallible and prone to error as every other human? So why can we trust them who wrote the Bible? These are good questions, indeed, but I would contend that we do not trust the writers, but instead we trust God. Scripture tells us not only that it is true, but also that God is sovereignly in control, and if these things are true, then it is reasonable to believe that God, through these writers, preserved His words to us and used these fallible men to do so. "And we also thank God continually because, when you received the word of God, which you heard from us, you accepted it not as the word of men, but as it actually is, the word of God, which is at work in you who believe" (1 Thessalonians 2:13).