Notoriously, during George W Bush’s presidency, Bush’s gut became the oracle of the state. Bush was distrustful of book learning and those with established expertise in a given area. When Bush made the decision to invade Iraq, and was subsequently confronted by a sceptical audience, Bush said that ultimately, he just knew in his gut that invading was the right thing to do. In CounterPunch, writer Rich Procter noted prior to the invasion: “Now we’re preparing to invade a country in the middle of the most volatile ‘powder-keg’ region on earth. We’re going to toss out our history of using military force only when provoked. We’re going to launch a ‘pre-emptive’ invasion that violates two hundred-plus years of American history and culture. We’re on the verge of becoming a fundamentally different kind of nation – an aggressive, ‘go-it-alone’ rogue state – based Bush’s gut.”

The invasion went ahead. A few months later, Senator Joe Biden told Bush of his growing worries about the aftermath. In response, Bush again appealed to the reliability of his “instincts”, as Ron Suskind reported in the New York Times Magazine:

“‘I was in the Oval Office a few months after we swept into Baghdad,’ [Biden] began, ‘and I was telling the president of my many concerns’ – concerns about growing problems winning the peace, the explosive mix of Shiite and Sunni, the disbanding of the Iraqi Army and problems securing the oil fields. Bush, Biden recalled, just looked at him, unflappably sure that the United States was on the right course and that all was well. ‘Mr. President,’ I finally said, ‘How can you be so sure when you know you don’t know the facts?’ Biden said that Bush stood up and put his hand on the senator’s shoulder. ‘My instincts,’ he said. ‘My instincts’ … The Delaware senator was, in fact, hearing what Bush’s top deputies – from cabinet members like Paul O’Neill, Christine Todd Whitman and Colin Powell to generals fighting in Iraq – have been told for years when they requested explanations for many of the president’s decisions, policies that often seemed to collide with accepted facts. The president would say that he relied on his ‘gut’ or his ‘instinct’ to guide the ship of state.”

How did Bush suppose his gut was able to steer the ship of state? He supposed it was functioning as a sort of God-sensing faculty. Bush believed that by means of his gut he could sense what God wanted of him. But how reasonable was it for Bush to trust what his gut was telling him?

Many would say “not very”. In The Ethics of Belief and Other Essays, for example, the philosopher W K Clifford famously insisted that “it is wrong, always and everywhere, to believe anything on insufficient evidence.”

People who believe despite not possessing good evidence that their belief is true are being downright irresponsible, thought Clifford. This quotation is often used to condemn those who believe in such things as the Loch Ness monster, angels, fairies and even God. Such beliefs, it is suggested, are not well-supported by the evidence. So it is wrong for people to believe them. So it was wrong for Bush to believe what he did, in the absence of good evidence.

The idea that it is, at the very least, unwise to accept claims for which we possess little or no supporting evidence is certainly widespread. For example, in A Devil’s Chaplain, Richard Dawkins writes,

“Next time somebody tells you something that sounds important, think to yourself: ‘Is this the kind of thing that people probably know because of evidence? Or is it the kind of thing that people only believe because of tradition, authority or revelation?’ And next time somebody tells you that something is true, why not say to them: ‘What kind of evidence is there for that?’ And if they can’t give you a good answer, I hope you’ll think very carefully before you believe a word they say.”

Let’s call the view that we ought not to accept any belief not well-supported by evidence evidentialism. Is evidentialism true?

Probably not. Evidentialism faces obvious difficulties. Perhaps the most glaring is this. Suppose I believe some claim A because I suppose I have supporting evidence B. But now ought I to believe that evidence B obtains? If evidentialism is true, it seems I ought to believe B obtains only if I posses, in turn, evidence for that – C, say. But then I should believe that C obtains only if there is, in turn, evidence for that, and so on ad infinitum. In short, evidentialism seems to entail that, before I adopt any belief, I must first acquire evidence to support an infinite number of beliefs – which, as a finite being, I can’t do. So Clifford’s injunction that I ought not to believe anything on the basis of insufficient evidence appears to have the disastrous consequence that I ought not to believe anything at all.

How might we escape this conclusion?

Before I address that question, let’s take a brief look at reliabilism, a theory of knowledge developed over the last half century or so, which would seem to entail that it is at least in principle possible (notice I don’t say likely) that some psychics, religious gurus and so on do indeed “just know” things by means of some sort of psychic or divinely-given sense. They do “just know” these things even if they don’t have any evidence to support what they believe. In which case, perhaps Bush might “just know” what God wants of him by means of his gut?

Here is a simple reliabilist theory of knowledge. In order for person A to know that P,

(i) P must be true

(ii) A must believe that P

(iii) A’s belief that P must be brought about by the fact that P via a reliable mechanism

What’s meant by a “reliable mechanism”? A reliable mechanism is a mechanism that tends to produce true beliefs. My sense of sight is a fairly reliable belief-producing mechanism. It allows my beliefs fairly reliably to track how things are in my environment.

Suppose, for example, someone puts an orange on the table in front of me. Light bounces off the orange into my eyes, which in turn causes certain cells to fire in my retina, which causes a pattern of electrical impulses to pass down my optic nerves into my brain, eventually bringing it about that I believe there’s an orange before me. Remove the orange and that will in turn cause me, by means of the same mechanism, to believe the orange has gone.

The same goes for my other senses – they are fairly reliable belief-producing mechanisms. Blindfold me and put me in a crowded street and my ears and nose will, in response to the sound of car horns and the odour of hot dogs, cause me to believe I am in a crowded street. Move me to a fragrant garden filled with singing birds and those same senses will cause me to believe I am in such a garden. My senses of sight, touch, smell, hearing and taste cause me to hold beliefs that tend accurately to reflect how things actually are around me.

I don’t say our senses are one hundred percent reliable, of course. Sometimes we get things wrong. They are occasionally prone to illusion. But they are fairly reliable.

Let’s now apply our reliabilist definition of knowledge. Suppose someone puts an orange on the table in front of me. I look at the orange, and so come to believe there’s an orange there. Do I know there’s an orange on the table?

According to our reliabilist, I do. The simple reliabilist theory says that if (i) it’s true that there’s an orange there, (ii) I believe there’s an orange there, and (iii) my belief is produced via a reliable mechanism (sight) by the presence of an orange there, then I know there’s an orange there.

Now here is an interesting consequence of this theory – a consequence very relevant to our discussion of psychic powers and George Bush’s gut. Notice, that, according to reliablism, in order to know there’s an orange on the table, I need not infer there’s an orange there. I need not arrive at my belief on the basis of good grounds or evidence. No evidence is required. All that’s required is that I hold the belief and that it be produced in the right sort of way – by a reliable mechanism.

Many contemporary philosophers accept some form of reliabilism (though they have developed it in various ways). You can now see why reliabilism might also appeal to, say, a psychic who believes she “just knows” things about the dead.

Suppose a self-styled psychic – call her Mary – finds herself believing that her dead Aunt Sarah is currently in the room with her. Also suppose, for the sake of argument, that Mary really does have some sort of reliable psychic sense, that dead Aunt Sarah really is in the room with Mary, and that Mary’s psychic sense is what is causing Mary to believe Aunt Sarah is present. Then, says our reliabilist theory, Mary knows that Aunt Sarah is in the room with her.

Mary doesn’t infer that Aunt Sarah is present on the basis of evidence. Mary just finds herself stuck with that belief that Aunt Sarah is present, caused as it is by her reliable psychic sense. Yet, says our reliabilist, despite the fact that Mary doesn’t possess any evidence that Aunt Sarah is present, Mary knows Aunt Sarah is there. In fact, were Mary to claim that she “just knows” that Mary is in the room with her right now, she’d be right.

Of course, that they do “just know” such things despite not possessing good supporting evidence is a claim psychics make on a daily basis. So, while few psychics have heard of reliabilism, reliabilism nevertheless opens up at least the possibility that these psychics are correct – they do know, despite not possessing any evidence.

“But hang on,” you may object. “Even if reliabilism is correct and Mary does know her dead Aunt is in the room with her, that is not something she ought to believe. The fact is, Mary is being downright irresponsible in just accepting at face value this belief that happens to have popped into her head. Clifford is still correct – she shouldn’t believe it. It’s still unwise for her to believe it.”

In her own defence, Mary might now appeal to a further principle. Surely, Mary may insist, if something seems very clearly and obviously to be the case, then, other things being equal, it’s reasonable to believe it’s true. It’s reasonable to take appearance at face value. For example, if it seems clear and obvious to me that there’s on orange on the table before me, then surely it’s reasonable for me to believe there’s an orange there.

This principle does seem intuitively plausible. And it entails that, if it seems just clearly and obviously true to Mary that her dead Aunt is in the room with her, then, other things being equal, it is reasonable for Mary to hold that belief. Whether or not she can provide any publicly available evidence.

Let’s now return to Bush’s gut. Bush believes he can directly know, by means of his gut, what God wants him to do.

Many people believe that they “just know” directly, rather than on the basis of evidence, that God exists and that, say, the Bible is true. Ask them why they believe, and they may give reasons and justifications of one sort or another. But typically, even if such grounds are provided, not much weight is placed on them. Most theists will say that they don’t believe on the basis of evidence. Rather, they “just know” God exists. They believe they experience God directly, perhaps in something like the way I just directly experience that orange on the table in front of me. To them, it seems perfectly clear and obvious that God exists.

Reliabilism seems to open up the possibility that some people might, indeed, “just know” that God exists. Suppose God has provided us with a sort of sensus divinitatis – a reliable, God-sensing faculty (in Bush’s case, that would be his gut). On the reliabilist view, it seems that a sensus divinitatis could provide such knowledge.

Moreover, a religious person might add, just as if it seems clearly and obviously true to me that there’s an orange on the table, then it is reasonable for me to suppose there’s an orange there, so if it seems clearly and obviously true to someone that God exists, then it’s reasonable for them to believe God exists. There’s certainly nothing wrong, or irresponsible, about them taking their experience at face value.

This view about religious experience has been developed by several contemporary Christian philosophers, chief among whom is Alvin Plantinga. Plantinga’s version is detailed, but the gist is essentially this: something like reliabilism is essentially correct, God has indeed given every one of us a God-sensing faculty or sensus divinitatis, and consequently, some of us can know, directly and without evidence, that God exists. Indeed, that God exists is an entirely reasonable thing for such people to believe if that’s very much how things clearly and obviously seem to them even after careful reflection.

Plantinga adds that, if there is a God, he probably would want us to know of his existence directly by means of such a reliable God-sensing faculty. So, if there is a God, then some of us probably do know by such means that God exists.

You may be wondering: “But if we all have a sensus divinitatis, as Plantinga supposes, why don’t we all enjoy such God experiences?” Because, Plantinga explains in his book Warranted Christian Belief, in many cases our sensus divinitatis has been damaged by sin: “Were it not for sin and its effects, God’s presence and glory would be as obvious and uncontroversial to us all as the presence of other minds, physical objects and the past. Like any cognitive process, however, the sensus divinitatis can malfunction; as a result of sin, it has been damaged.”

We have seen how the reliabilist theory of knowledge seems to open up the possibility that some people might “just know” that their dead relative is in the room with them, or “just know” that God exists. We have also seen that evidentialism has been challenged, and that, according to Plantinga and others, it can be entirely reasonable for people to take their religious experiences at face value. Let’s now begin to assess these claims.

In fact, I find reliabilism plausible. I suspect that some version of reliabilism may well be correct. Let me also be clear that I do not rule out in principle the possibility that some people might be equipped with reliable psychic powers, or a sensus divinitatis, or whatever.

I’ll also concede that evidentialism is probably false, and that, generally speaking, it is indeed reasonable for us to take appearances at face value. If it seems just clearly and obviously the case that there’s an orange on the table in front of me, well then, other things being equal, it’s reasonable for me to believe there’s an orange on the table in front of me.

However, I remain entirely unconvinced that anyone who claims to “just know” that the dead walk among us, or that God exists, knows any such thing. Not only do I think the rest of us have good grounds for doubting their experience, I don’t believe it’s reasonable for them to take their own experience at face value either. I’ll explain why by means of what I call the case of the mad, fruit-fixated brain scientist.

Suppose Jane is shown what appears, quite clearly and obviously, to be an orange on the table in front of her. Surely then, it is, other things being equal, reasonable for Jane to believe there’s an orange there.

But now suppose the orange is presented to Jane in a rather unusual situation. Jane is one of several visitors to the laboratory of a mad brain scientist with a weird fruit fixation. She, like the other visitors, is wearing an electronic helmet that can influence what happens in her brain. From his central computer terminal, the mad brain scientist can, by means of these helmets, control what people are experiencing. He can create vivid and convincing hallucinations.

The scientist demonstrates this by causing one of the visitors to hallucinate an apple. There’s much hilarity as the victim tries to grab for the fruit that’s not there. The visitors are then invited to wander round the lab where, the scientist tells them, they may experience several other virtual fruits. Jane then comes across what appears to be an orange on a table. Now, as a matter of fact, it is a real orange – one that fell out of someone’s packed lunch bag. Jane’s faculty of sight is functioning normally and reliably. This is no hallucination.

Now ask yourself two questions: (i) does Jane know there’s an orange on the table? And (ii) is it reasonable for Jane to suppose there’s an orange on the table?

Intuitively, it seems Jane doesn’t know there’s an orange present. After all, for all Jane knows, it could be one of the many hallucinatory fruits she knows about. But what would a reliabilist say? Well, sight is generally a reliable belief-producing mechanism, and sight is what’s producing her belief. So some reliabilists may say that, yes, Jane does know. On the other hand, very many reliabilists say that, while in a standard environment, sight is reliable, it isn’t reliable in other kinds of environment, e.g. the kind of environment in which we will often as not be deceived by visual hallucinations. But then it follows that, because she is in just such an environment, Jane doesn’t know.

Now let’s turn to question (ii), which is the pivotal question:is it reasonable for Jane to believe there’s an orange before her?

Surely not. Given Jane knows that she is in an environment (the mad brain scientist’s laboratory) in which people regularly have compelling fruit hallucinations (indistinguishable from real fruit experiences), Jane should remain rather sceptical about her own fruit experience. For all she can tell, she’s probably having a mad-scientist-induced fruit hallucination.

I draw two morals for religious experience.

First of all, even if reliabilism is true, and even if some of us do have God-experiences produced by a sensus divinitatis, it remains debatable whether such people know that God exists. If human beings are highly prone to delusional religious experiences that they nevertheless find entirely convincing, then, even if, as a matter of fact, I happen to be having a wholly accurate religious experience revealing that, say, the Judeo-Christian God exists, it’s by no means clear I can be said to know the Judeo-Christian God exists, any more than Jane, coming upon a real orange in the brain scientist’s lab, can be said to know that there’s an orange on the table in front of her.

Second, and more importantly, even if it’s true, because of my religious experience, that I do know that the Judeo-Christian God exists, surely it still isn’t reasonable for me to take my experience at face value. For I find myself in a situation much like Jane finds herself in the brain scientist’s lab. Even though it looks to Jane clearly and obviously to be true that there’s an orange on the table in front of her, Jane should, surely, remain pretty skeptical about whether there’s actually an orange there, given that, for all she knows, she might very easily be having one of the many delusional fruit experiences currently being generated in the lab. Jane would be foolish to take appearance at face value. Similarly, if I have good evidence that a high proportion of religious experiences are delusional – even the most compelling examples – then surely I should be equally skeptical about my own religious experiences, no matter how compelling those experiences might be. I would be foolish for me to take my experiences at face value.

A similar moral might be drawn about psychic experiences. If most – including even the most compelling examples – are delusional, then it’s debatable whether the psychic can be said to know. However, even if the psychic can be said to know, if they’re aware that many such experiences are delusional, then it surely isn’t reasonable for them to take their experience at face value.

Stephen Law is Senior Lecturer In Philosophy at Heythrop College.  His book, Believing Bullshit: How Not To Get Sucked Into An Intellectual Black Hole, was published by Prometheus, 2011.