A common reaction from those challenged to provide us with evidence that there are fairies at the bottom of the garden, or that the dead walk among us, or that God exists is to say ‘But…but…I just know!’ Defenders of these beliefs often believe they have some sort of special, direct awareness that allows them to know these things. Many who believe in God suppose they have a sort of God-sense or sensus divinitatis by which God reveals himself to them. Psychic Sally and others who believe the dead walk among us believe they have a spirit sense by which they can sense the presence of, and even communicate with, the deceased.

Now, interestingly, some popular views in epistemology allow that they might ‘just know’.

Consider the kind of ‘externalist’ theories of knowledge which say that, in order to know that so-and-so is the case, it is sufficient that, say, your belief be true and that it be hooked up to the state of affairs that makes it true in the right sort of way. What is ‘the right sort of way’? Well that depends on the precise theory of knowledge in question, but a common suggestion is that your belief must be produced by a generally reliable belief-forming mechanism. Sight, memory, and so on are thought to be such reliable mechanisms for forming true beliefs.

So, for example, I believe there's an orange on the table in front of me. Now suppose that my belief is brought about by an orange on the table via a reliable belief-forming mechanism, such as sight. Then I can know there's an orange there.

Now notice that on such ‘externalist’ theories, there's no requirement that, in order to know there's an orange there, I must know my belief is produced in the right way sort of way. I don't need to know anything about sight or its reliability or its role in producing my belief in order to know there's an orange before me. Just so long as my belief is produced in the right sort of way, I can know.

But of course such theories open the door for those who suppose they ‘just know’ that God exists, that the dead walk among us, or that fairies exist to say, ‘Me too!’ The spiritualist can say, ‘It just really seems to me the dead walk among us, and if they do – if my belief really is produced by some sort of reliable spirit-sense – then I know the dead walk among us.’ And the religious person can say, ‘It just really seems to me that God exists, and, if he does and if he is revealing to me his presence by some sort of reliable sensus-divinitatis or God-sense, then I know that God exists.’

How should we respond to this sort of claim? It can be tempting to say ‘But, where's your hard evidence to support these beliefs? If you can't present it, you really shouldn't believe!’ However, this sort of ‘evidentialist’ view is also now rejected by many epistemologists. Surely, if it really seems to me that I ate toast for breakfast, then it's reasonable for me to believe I did even if I can now provide no evidence at all that I did (the washing up is done and all the evidence is gone). Indeed, surely I still know I had toast for breakfast even if I can't point to any supporting evidence. All that's required is that my belief be produced by my reliably-functioning memory. But then similarly, surely someone could reasonably believe, and indeed know, that God exists even without evidence? This is currently a popular line of thought among Christian philosophers and apologists.

I think a better response to those claiming to ‘just know’ God exists or that the dead walk amongst us would be to point out that there is good evidence these beliefs are false (if such evidence exists). In addition notice that, even if there weren't good evidence these beliefs are false, saying ‘I just know’ won't do if it has been pointed out to the subject that there is good evidence that their belief is not a product of a reliable mechanism. If I seem to remember having toast for breakfast, it's reasonable for me to believe I did. But it's no longer reasonable for me to believe I did once it is pointed out to me that I have been given a drug that often causes false breakfast memories. Then I should no longer trust my memory. It would be unreasonable for me to continue to believe given only my apparent memory.

But now isn't there plenty of evidence that we human beings are highly prone to false beliefs in invisible person-like agents (ghosts, gods, fairies, spirits, sprites, etc.) when those beliefs are based on such subjective experiences? If so, this evidence should lead those who believe in gods, ghosts and so on solely on that basis to no longer trust their subjective experiences of such things. Those who continue to believe on just that basis would do so unreasonably. Saying, ‘But…but… I just know’ would, in this case, be irrational. It would remain possible that they do still know (if their belief is produced by a reliable god- or spirit-sense). But it would no longer be reasonable for them to suppose they know.