Testimony of Miracles cannot support Religious Beliefs
This argument is largely taken from David Hume’s “Of Miracles”, though taken in a different direction.
There are two types of possible miracles: ones you directly experience, and ones that other people directly experience. If you directly experience a miracle, then you have good reason to believe in it. If not, then you must rely on the testimony of others to believe it.
Here’s the problem: how can you know that testimony of miracles is reliable, and not false? One way is to reproduce the miracle, so you can directly experience it. If not, then you must rely on the validity of the testimony. So, should you expect the testimony of miracles to be true?
In logical terms: The truth of the proposition “X told me a miracle happened” is sufficient for the truth of “I should believe a miracle happened”.
Obviously, this approach will not work. It is clearly true that people have lied about miracles and their experiences. If you took “testimony” as sufficient for “I should believe it”, then you would be stuck believing every story from every belief system imaginable. Some of these stances would be logically contradictory.
So, it is clear that “X told me a miracle happened” is not, by itself, sufficient for “I should believe a miracle happened”. So, what other proposition’s truth could be sufficient, or perhaps jointly sufficient with the first proposition?
The first option would be “it can be proved through empirical evidence”. However, this condition would not be applicable to any case of miracles. You can’t use physical, non-magical evidence to infer that a magical event took place. The second option might be “more than one person told me”, but this would fail for the same reason as the original proposition: millions of people have claimed to be directly contacted by different deities. They cannot all be right, unless there are multiple gods who are completely unaware of each other.
Instead of looking at what potential propositions could help (as they are all dead ends), I want to look at what people actually use in practice to determine whether or not a testimony of a miracle is believable or not. This practical approach inevitably results in one answer: because the testimony is consistent with their already held religious beliefs. Meaning a Christian will believe someone who said Jesus preformed a miracle for them, but not someone who claimed it was Vishnu who helped them out.
Back to logical form, this means that in practice, the truth of two propositions ”X told me a miracle happened” and “the miracle is consistent with my religious beliefs” are jointly sufficient for the truth of “I should believe a miracle happened”.
The problem: if this is the only way people can, in practice, believe miracles, then miracles cannot give any support whatsoever for religious beliefs. In order for the miracles to be supported, you already need the assumed truth of your religious beliefs. If your religious beliefs aren’t assumed to be true, then there is no reason to believe some miracle testimonies over others. However, if you assume your religious beliefs, nothing that is derivable from that assumption can be used to provide support for the truth of your religious beliefs. To claim it would be, would be begging the question-already assuming the truth of the conclusion that you are trying to prove.
In short, miracles cannot be believed to be true unless you already assume the truth of a belief that would make that miracle possible. Therefore, there are no miracles that are believable without the assumption of its respective religious belief. Because of this, miracles necessarily cannot provide support for religious beliefs, as to do so would be begging the question.