There are many people who are religious. But most of them are philosophically uninteresting, because most people are irrational, at least some of the time. So given people who tolerate irrationality it is not surprising if they can accept faith. What is more interesting is the few rational people who are religious, since rational people must construct arguments for why they are right to believe in religion, if they are to be consider themselves rational. Specifically I am interested in people who claim that they have evidence for their religion, but I will discuss a few other arguments before I get there, starting from the least plausible.
The least plausible argument for religion that I have heard put forward by rational people is that without religion the universe doesn’t make sense. To which we are naturally forced to ask: why must the universe make sense? Followed by: religion makes sense? Perhaps what people who put forward this argument are really driving at is the next argument for religion. Which is that religion makes them feel good, or is in some other way good for people, a pragmatic argument. This argument would hold water if people sincerely thought that the truth was less important than feeling good. But people usually don’t demonstrate this preference. Surely it would make us feel better if we thought that we had a million dollars in our accounts, but no matter how good it might make us feel we shouldn’t, because it isn’t the truth. And as for the idea that religion is somehow beneficial to society, say by providing moral guidance, well the evidence seems to indicate that religion has little or no impact on how well people behave. And you certainly don’t see atheists bombing abortion clinics or persecuting homosexuals. (I know, you are thinking: my religion doesn’t do that. And I should hope not. But that doesn’t mean it has a positive effect either. In all likelihood you would be just as ethical as an atheist, and instead of worrying about god you would worry about the cops.)
So let me turn to the serious arguments for religion, both of which turn on evidence. The first is the claim that a person has had personal evidence for the validity of their religion / spiritual forces / whatever. If you confront such a person with arguments against religion they will simply claim that they have evidence, and although that evidence may not be convincing to you (as you might think that they are mistaken), it is convincing to them. And so their faith is unshakable. Often arguments of this sort are accompanied by a story of something good happening, possibly as a result of prayer, followed by the conclusion that it was god’s work. I don’t think such people are lying, I think that they are victims of a well-known phenomenon called confirmation bias. Confirmation bias is a mistake in reasoning that we are prone to make without even knowing that we are making it, and no matter how rational or intelligent we may be we are still be misled by it (although knowing that confirmation bias exists allows us to correct for it sometimes). Specifically confirmation bias is the tendency of people when examining evidence for and against a conclusion they are invested in (they want it to turn out one way or the other) give more weight to the evidence that supports the conclusion they favor, unconsciously. For that one event that convinces people that god exists there are millions of others in which god could have intervened, perhaps should have intervened, but didn’t. And when you take the good and the bad together that one unlikely event doesn’t seem that unlikely anymore. Sure unlikely events are rare, but given long enough we will probably all experience a few of them. And so realistically that one event in isolation isn’t evidence for anything.* Unfortunately confirmation bias leads people to give these events more weight than they deserve, and thus they become convinced, falsely, that their beliefs are supported by their experiences. You can read more about confirmation bias here.
So personal evidence for religion isn’t as reliable as it could be. But perhaps there is public evidence, specifically miracles of one kind or another. And I admit there are rare cases of miracles with a fair number of witnesses whom one would usually consider reliable (not many, but some). Are these “miracles” evidence for religion? Well some might think that they are, but that is not a rational position, for reasons first given by Hume. First we must consider what a miracle is. Certainly it must be an event that is extremely unlikely, because if there were a reasonable chance of the event happening then we wouldn’t call it a miracle, we would simply consider it unusual. We must also consider that no matter who a witness is, and no matter how reliable they are, that there is a probability that they are mistaken, deluded, lying, conspiring, ect, in essence the probability that they would tell us the miracle happened without there being a real miracle. Of course when we consider the probability of a group of people telling us that a miracle happened when it did not the probability is reduced even further (although not as reduced as one might think, there are powerful pressures that cause people who talk about events to come to honestly believe the same account, even if they originally believed differently). We must then compare the probabilities of the two events, the probability of the miracle occurring and the probability of all the witnesses incorrectly reporting it to us. And since miracles are so unlikely, and because groups of people have known to be mistaken in the past (it happens all the time actually), it is more likely that the witnesses are in error. And thus we have no rational reason to believe that the miracle happened. Of course if well-documented miracles happened regularly the situation might be reversed, but unfortunately for religion “reliable” miracles don’t happen often enough (more frequently than we would expect a group to be mistaken or lying), or worse happen for other religions, and so miracles can’t be considered evidence for religion, even a vague theistic or spiritualist one.
* Interesting side note: have you noticed that this argument is less and less likely to be used as we consider wealthier groups of people. Specifically poorer people are very likely to give this argument, citing something unusually good happening to them, while the rich are much less likely. This is not because the poor are stupid. I suspect that the real reason is because if your quality of life is lower the rare fortunate event stands out that much more, seeming more miraculous, while the rich are used to good things happening to them, and thus consider it par for the course.