It is sometimes tempting to appeal to mystery to get oneself out of intellectual hot water. Suppose a scientist offers a science-based criticism of Mary's paranormal beliefs. In response Mary might say something like this: ‘Ah, but this is beyond the ability of science and reason to decide. You, Dr Scientist, are guilty of scientism, of assuming science can answer every question.’ Mary might follow this response up with a quote from Shakespeare's Hamlet: ‘There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.’
Of course, most scientists admit they can't explain everything. There probably are questions science cannot answer. Mary attempts to protect her beliefs by placing them in this category of beliefs science can't touch. She draws a veil across reality and says, ‘You scientists can apply your methods this far, but no further.’ Behind the veil Mary might place angels, psychic powers, fairies, dead relatives, and so on. She might also insist that, while such phenomena lie beyond the bounds of scientific investigation, there are special people – mediums, mystics, gurus, and so on – who can see, if only dimly, through the veil and so inform us about what lies beyond.
However, many of the claims made about things supposedly behind Mary's veil do in fact have empirically observable consequences and that does make them scientifically testable.
Take the claim the crystals have a beneficial effect on our mental states. Psychologist Christopher French at Goldsmiths, University of London, ran an experiment into the effects of crystals to explore claims that holding real crystals from a New Age shop while meditating has a powerful effect on the psyche, more so than just holding fake ones. French found no difference in participants using real and fake crystals. This was good evidence that the effects people report is down to the power of suggestion, not the crystals.
Of course, this study provoked comments such as: ‘Not being able to prove the existence of something does not disprove its existence. Much is yet to be discovered.’ This was just a smokescreen. Still, so familiar is the mantra, ‘This is beyond the ability of science to decide’ that it can be effective at lulling people back to sleep – even when they have been stung into entertaining a doubt for a moment or two.
Some things may be beyond our understanding, and sometimes it's reasonable to appeal to mystery. If you have excellent evidence that water boils at 100 °C (at one atmosphere), but on one occasion it appeared it didn't, it's reasonable to attribute that to some mysterious, unknown factor. It's also reasonable, when we have a theory that works but we don't know how it works, to say that this is currently a mystery. But the more we rely on mystery to get us out of intellectual trouble, or the more we use it as a carpet under which to sweep inconvenient facts, the more vulnerable we are to deceit, by others and by ourselves.