According to the argument from religious experience, we are supposed to accept religious experiences as evidence for the supernatural, in the absence of positive reasons for thinking that experiencers are deluded. However, this argument is unconvincing, for the following reasons:
Firstly, in the cases of people who claim to have communicated with God, further scrutiny never uncovers any convincing evidence. None of these experiences has ever been independently proved beyond any reasonable doubt to be true – they can always be explained by more mundane, non-supernatural means.
Secondly, religious experience is present in many different religions, and produces largely contradictory and inconsistent claims. As an extreme example, the Yorkshire Ripper claimed that God told him to murder prostitutes. If we are to allow claims of personal religious experience, how are we to determine the false from the supposedly true?
Thirdly, religious experiences typically generate claims that cannot be corroborated by independent evidence (e.g., metaphysical claims, clichés, banalities etc.).
Finally, no new and important scientific, mathematical, or medical knowledge is ever revealed. If an experiencer was ever told something of this nature that is clearly beyond our current knowledge, then this might suggest a phenomenon that needs explaining. Alas, this does not happen.
And, how would we investigate any such supposed claims? Well, for a start, we need to look for reliable, independent evidence that there is indeed some unexplained phenomenon going on here. That’s even before we address the question of whether this phenomenon is in any way supernatural in origin. So far, none of the supposed experiences has even passed the first test.
Theists often cry foul at this point. This type of experience is not amenable to scientific investigation, they say. In their minds, the world in split into those things that can be investigated scientifically, and those that cannot. Religious experiences definitely fit into the latter category, they think. However, under these rules, anybody would be entitled to claim anything that they want, so long as they then rule it off limits to scientific enquiry. I might say that I can communicate telepathically with rocks, or that I can make myself invisible (of course, only when nobody is present, and there are no cameras recording me), or that I can travel through higher dimensions. Obviously, none of these supernatural phenomena is amenable to scientific enquiry, so you’ll just have to take my word for it! This way of trying to fathom the universe is a non-starter.
But even theists don’t apply their logic universally. In general (in the western world), when they are ill they don’t call for an exorcist to expel their demons (even though demons could theoretically be the cause of illness, if we were ignore all of the scientific explanations and evidence); when their car breaks down, they don’t call for a witch doctor to utter some incantation over it (even though, again, this could be the best choice of action if we ignore all of the evidence and rational explanations). Why is this? One could say that it is hypocrisy. But, I think that it goes deeper than this. I think that they know, deep-down, that the world doesn’t work that way, and that the scientific and evidentially-based approach is best choice. They just ask for special pleading in the case of the god of their chosen superstition.
Hume's dictum is apposite here:
"When anyone tells me, that he saw a dead man restored to life, I immediately consider with myself, whether it be more probable, that this person should either deceive or be deceived, or that the fact, which he relates, should really have happened. I weigh the one miracle against the other; and according to the superiority, which I discover, I pronounce my decision, and always reject the greater miracle. If the falsehood of his testimony would be more miraculous, than the event which he relates; then, and not till then, can he pretend to command my belief or opinion."
In other words, when someone claims the miraculous, is it more likely that they are right or, rather, that they are mistaken or lying?
And, on the subject of evidence, some may hold that this is just question-begging and ultimately illusory. However, how many of them would have the courage of their convictions and call for a complete overhaul of the legal system, to create one in which no evidence is ever examined? How would crimes be tried? That’s a good question. Maybe guilt would be determined by the roll of a die, or by the judge communing privately with god. Then again, maybe not!
The mistake here is to demand absolute certainty in our beliefs. In the real world, this can never be achieved, even in principle. However, predictions made by our beliefs can be more or less in agreement with the evidence; beliefs can be more or less powerful in their explanatory power; and they can be more or less parsimonious. Our understanding of the universe as expressed by our scientific theories is always going to be provisional in nature, and is always subject to further revision. However, to just throw our hands up in the air in resignation at this realisation is futile. Application of reason and the scientific method is still our best hope of making progress in this endeavour. Our attempts to fathom the universe are definitely still a ‘work in progress’, but there is no value in allowing supernatural explanations to fill the gaps in our knowledge, as this has always proved to be premature so far.