Why I'll keep on flossing, thank-you.

You should floss your teeth everyday.

Knowing how much importance I place on evidence, and given the recent media hype spawned by a story by the Associated Press about the paucity of good quality evidence supporting that recommendation, you might be tempted to call me a hypocrite.

But you’d be wrong.

If you’ve been reading this blog, you’d also know that I fully recognize that we most often have to make decisions in the absence of complete or even good information (see here). And besides, as nice as it would be, we don’t need the highest quality evidence - multiple, consistent, well-conducted randomized controlled trials (RCTs) -  to provide a reasonable answer to every question.

So what is the state of the evidence regarding daily flossing? You could find that out for yourself – no media craze required – at the Cochrane Collaboration (which I’ve written about before here) who wrote:

"Twelve trials were included in this review which reported data on two outcomes (dental plaque and gum disease). Trials were of poor quality and conclusions must be viewed as unreliable. The review showed that people who brush and floss regularly have less gum bleeding compared to toothbrushing alone. There was weak, very unreliable evidence of a possible small reduction in plaque. There was no information on other measurements such as tooth decay because the trials were not long enough and detecting early stage decay between teeth is difficult."

And here's what they concluded:

"There is some evidence from twelve studies that flossing in addition to toothbrushing reduces gingivitis compared to toothbrushing alone. There is weak, very unreliable evidence from 10 studies that flossing plus toothbrushing may be associated with a small reduction in plaque at 1 and 3 months. No studies reported the effectiveness of flossing plus toothbrushing for preventing dental caries."

It should be no surprise that there are no randomized trials reporting a reduction in cavities (dental carries) among flossers compared to non-flossers. Such a study would require that large numbers of subjects be randomized and followed for years (since it takes years for carries to develop). Large, long-term studies are costly and labor intensive, and that's why they haven't been done. Who's going to pay millions of dollars to do those studies? Are you willing to cough up some money for the cause?

Perhaps the industry that profits from the manufacture of dental floss should cover the costs, but why would they when the available evidence is enough to reasonably conclude that regular flossing prevents gum disease, which is really enough to recommend it? Even if that's all that it does, you should be flossing. Never mind that there isn't evidence showing that it prevents cavities.

This is an especially important question among people like me with valvular heart disease (VHD). Gum bleeding that permits oral microbes access to the bloodstream is an important cause of infectious endocarditis: a life threatening infection on heart valve tissue. Among the most common causative microbes are oral bacteria that get into the bloodstream by way of gum injury and micro bleeding that occurs throughout regular daily life (1,2).

When I was diagnosed with VHD about 4 years ago, I started flossing every day. Prior to that, I was like Margaret Wente (whose inflammatory piece in the Globe and Mail sparked my desire to write this post), which is to say that I only flossed a day or two before seeing my dentist, and when I did, my gums always bled. But since flossing daily, my gums hardly ever bleed, and haven’t bled at all at my last 2 dental visits. I’m living proof that flossing prevents gingivitis and there is plenty of other anecdotal evidence like mine to add to the already existent and reasonably good higher-quality evidence that it does.

Another widely reported anecdote that I can speak to: despite brushing twice a day, that string used to have quite a smell when I was finished, but after a few weeks in the habit, the foul scent was gone. Preventing bad breath is another terrific reason to floss your teeth daily, don't you think?

Now, one caveat: all of my comments refer to regular (ie. daily) flossing. Intermittently flossing and stopping will likely lead to more gum bleeding because the gingivitis that causes the underlying bleeding just returns in between flossing stints. That could actually be harmful, since everybody is at risk of endocarditis (though not as at high a risk as people with VHD). But other than that, the potential risk of daily flossing is almost certainly astronomically low.

Just as we don’t need a RCT of parachutes for jumping out of airplanes, we also don’t need anymore RCTs of flossing. As tempting as it may be - because I know how unpopular the idea of regular flossing is to most people - you should not mistake an absence of evidence (or a paucity of evidence, in this case) for evidence of absence. I'm sufficiently convinced that daily flossing is having a positive impact on my oral hygiene, and perhaps even to my overall health, and you should be too.

The stakes may not be as high for you as for me, and you may reasonably decide that a reduction in gingivitis is not worth daily flossing for you, which would be fine because you'd be making a decision based upon a reasonable and well-informed interpretation of the evidence. But please, do not make the mistake that Margaret Wente and others in the media have made, which is to conclude, because it's the conclusion that they like and/or that they think their readers will like, that we should all stop flossing because there is evidence that it doesn't do any good.

That would not be fine at all.


1. Lockhart PB, Brennan MT, Sasser HC, Fox PC, Paster BJ, Bahrani-Mougeot FK. Bacteremia associated with toothbrushing and dental extraction. Circulation 2008;117:3118–3125

2. Veloso TR, Amiguet M, Rousson V, Giddey M, Vouillamoz J, Moreillon P, Entenza JM. Induction of experimental endocarditis by continuous low-grade bacteremia mimicking spontaneous bacteremia in humans. Infect Immun2011;79:2006–2011.

Common sense is too common

The snow has finally stopped falling and you're pleased to be inside, driveway all shovelled neatly (first one on the block!), the aroma of a fresh pot of coffee permeating your home. Too bad for you that the squeezing sensation in the centre of your chest that kind of niggled while you were outside has just returned, but this time with a vengeance. Your wife calls 911 because the worried look on your face is actually worse than hers. What's the first thing paramedics will do when they arrive and learn that you're having chest pain? What's the first thing you probably want them to do?

Before even giving you an aspirin to chew, they'll probably strap on nasal prongs and give you some oxygen. After all, if you're having a heart attack, the problem is that the supply of blood, and therefore of good ol' oxygen, to your heart muscle is being choked off by a blood clot in a heart artery.

What could go wrong by giving a supplement of a natural substance that all our cells need to survive and of which those cells are being deprived?

Lots, apparently. Just click here to see the results of a clinical trial that randomly assigned 638 patients with chest pain to receive supplemental oxygen or not. Four hundred and forty one of them turned out to be having heart attacks and during followup, compared to those who just breathed ambient air, those who got the oxygen had larger heart attacks, more recurrent heart attacks, and more cardiac arrhythmias.

Traditional Chinese Medicine Store

Now just think, if oxygen turns out to be bad for you in the midst of a heart attack - a natural and "common sense" treatment given a basic understanding of the situation - what other supplements that are natural and appeal to common sense might be bad for you, too?

Supplement Store

The available data make a strong enough case to stop routinely providing supplemental oxygen to patients having chest pain and heart attacks. A time honoured treatment should no longer be employed. There is a long list of medical therapies established by common sense that are no longer offered because they've been shown in clinical trials to be ineffective or harmful (and it's an amazing list that you really should click on and see so here's another chance if you missed it before).

Tell me this: when was the last time that a supplement, herbal, or homeopathic treatment was tested by those practitioners in a clinical trial and pulled from the shelves?

Homeopathy Store

Another timely example of the failure of common sense is screening for cancer. If you have a test that can detect cancer, applying it to populations should reduce premature deaths. Simple, right? But the situation for screening is much more complicated than it seems and, in fact, screening the general population for cancer, including breast, lung, colon and prostate cancer, is probably a huge waste of time, effort, worry, and money (with the possible exception of pap smears for cervical cancer). Not only that, it probably causes more harm than good, and it's a practice that should stop. The same is true for the annual physical examination, which is going the way of the Dodo. Why? Because skeptical people put these common sense notions to the real test of randomized trials and the results weren't what common sense had predicted.

Common sense tells us that because something seems like it should work, it does work, but it's time to get humble, to became skeptical of common sense. It's time to admit that many things are far more complicated than they seem. I know that may make some people feel small and insignificant, but that's really not necessary. Evidence makes us powerful. Experts aren't necessarily smarter than you. Real experts just know the evidence better than others. By learning how to find and assess the evidence, you can become powerful, too. An easy way to get to the best understanding of the available health-related evidence is to use Cochrane, a global non-profit, non-governmental organization that you can read all about at Wikipedia here. Search your health query and Cochrane is your friend.

Voltaire said that common sense is not common. On the other hand, it seems far too common to me. In everything from philanthropy to economics, from politics to education, and beyond, what we need is less common sense, and more high quality evidence.

Are there more things in Heaven and Earth, Horatio?

Is the supernatural beyond reason and evidence, safely protected from human investigation? And is God, a supernatural entity, therefore, off limits for "empiric and rationalist" considerations?

I'm going to begin by answering the first question as it might relate to the alleged healing powers of acupuncture. Then, I'll draw those threads together and show how the same considerations actually apply to God, too.

The idea behind acupuncture is that the pathophysiology of the disorder being treated includes an unhealthy bodily flow of Qi ('Chi') - said to be a type of living or vital energy.   The placement of subcutaneous needles in specific locations is supposed to restore the normal flow of Qi, helping to heal the disorder in a biologically active way.

Qi is an ancient and intuitively appealing concept. There must be some important difference between living organisms and dead ones (or inanimate objects), after all, so why wouldn't it be a mysterious quantity and why not call it a type of energy since, in other circumstances, energy is invisible except for the things it makes happen? But we now know better. Vitalism has been thoroughly and completely discredited by science. Life is driven by the usual types of energy that are all well described - the same kinds of energy that drive all chemical reactions, only in the case of life, those reactions maintain homeostasis for at least enough time for a given species to reproduce. No additional or special type of energy is required to explain life, and no reputable or serious biologist thinks otherwise, anymore.

Nevertheless, millions of people still believe in Qi and acupuncture. "Science just hasn't discovered a way to detect or measure Qi, yet," they tell us. But that is a big, smelly, red herring.

It actually doesn't matter whether we can detect or measure Qi itself, for we are told that Qi and its manipulation has effects in this world that are measurable. We are told that acupuncture has the measurable effect of healing people. Accordingly, we can conduct randomized controlled trials where people are randomly assigned to real or sham acupuncture treatments (where the needles don't actually penetrate the skin and are placed at random locations by non-acupuncture practitioners). If acupuncture works, we can make a prediction: the people getting real acupuncture treatments should improve more quickly and/or more thoroughly than the people getting sham acupuncture treatments. It doesn't matter one iota that we can't measure Qi or it's flow patterns directly. All that matters is that we can predict and measure the alleged effects of Qi here and now, in the natural world.

Well, studies of this kind have been done over and over and I'm afraid that it doesn't look good for acupuncture. The outcomes in the 2 groups are largely indistinguishable. One clearly shouldn't think of acupuncture as doing anything biologically active beyond the power of suggestion. While this doesn't disprove the existence of Qi, it certainly proves that acupuncture as a way of beneficially manipulating Qi is useless. Maybe there are other ways of doing so, but until those are discovered, the idea of Qi adds nothing to our understanding of illness and health, and there's absolutely no reason to believe that it does exist.

It's possible that Qi has nothing to do with anything in the natural world. Perhaps it's purely supernatural. But, if it is, then it's of no consequence here, and should be of no concern to anybody; the whole idea is without meaning. If it does have consequences in the natural world, then those consequences should be measurable or detectable.

And so it is with all supernatural claims, including the existence of the Christian God. Maybe we can't directly detect the Christian God, but we can reason from God's alleged qualities to predictions about the way the world ought to be, and then look for evidence of whether the world is as we'd expect, or not. We would expect a universe where the Christian God exists and is omnipotent, morally perfect, perfectly loving, desirous of a personal relationship with us, etc. to look quite different from a world where no such God exists. For example, if the Christian God exists, we wouldn't expect any gratuitous natural suffering, yet we see a world that appears to be overflowing with it. We wouldn't expect there to be billions of non-believers clustered within borders explained by natural and haphazard factors like politics and conquest. If evidence gathered in the world is better explained by the non-existence of God, then the existence of God should seem much less likely to us. At the very least, it should cause us to become very skeptical of the alleged qualities that those failed predictions are based upon. There are very many predictions made by Christian theism that can be tested here on Earth, and I'm afraid that, like acupuncture, the situation doesn't look good at all.

Perhaps the Christian God doesn't exist, but a different God who lives entirely in a theoretical supernatural world does. Perhaps we know nothing about the qualities and capabilities of such a God and he never interferes in this world in any way. This pretty much describes what deists believe. This type of God really is beyond investigation by reason and evidence, but what a useless belief! A universe where this God exists is no different in any way than one where such a God doesn't exist.  It might as well not exist at all.

This reminds me of the parable of the invisible gardener, by John Wisdom:

"Two people return to their long neglected garden and find, among the weeds, that a few of the old plants are surprisingly vigorous. One says to the other, 'It must be that a gardener has been coming and doing something about these weeds.' The other disagrees and an argument ensues. They pitch their tents and set a watch. No gardener is ever seen. The believer wonders if there is an invisible gardener, so they patrol with bloodhounds but the bloodhounds never give a cry. Yet the believer remains unconvinced, and insists that the gardener is invisible, has no scent and gives no sound. The skeptic doesn't agree, and asks how a so-called invisible, intangible, elusive gardener differs from an imaginary gardener, or even no gardener at all."

I'm afraid that existential questions seem to always and only boil down to reason and evidence. When there is reason and evidence, a conversation can be had about their merits and meanings.  When reason and evidence are unavailable in either principle or practice, we have a meaningless claim that terminates the conversation.

Believing despite insufficient reason and evidence - believing on faith - is propped up as being incredibly valuable, but why? What's so great about faith? It seems to me that in every domain of human discourse other than religion, believing on faith is rightly frowned upon. Would you cross a street on faith without looking to see if a bus is coming? Look at what believing in the existence of God on faith gets us: thousands of Gods and traditions most of which are mutually exclusive, and balkanized  doxastic communities with a horrible and ongoing history of intolerance, discrimination, and slaughter in the name of those beliefs. This is supposed to be the Zenith of human understanding and the path to the most important 'truths' in the universe? What could the word 'truth' possibly mean in that sentence without reason and evidence?

There may well be plenty more in Heaven and Earth than is dreamt of by reason and evidence, but without them, I'm afraid it's all just "Words, words, words." (Shakespeare - Hamlet).

There are more things in Heaven and Earth, Horatio...

Keanu Reeves as the Prince of Denmark during Winnipeg's MTC production in 1995. Check out that passion.

I recently had a nice discussion with some friends about the challenges of identifying as Catholic given numerous problems that flow from standard Catholic doctrine combined with the hypocrisy and scandal within the organization. Along the way, I received this comment:

“You seem to operate out of a rationalist-empiricist framework. And there is of course nothing wrong with that when one is considering matters subject to the analytical benefits of this sort of world-view. But I suggest that there is plenty of human endeavor and human interest in matters not well suited to this sort of analysis. I mean, would you really mock John Keats because figures on an urn are not really “frozen” there? Or would your smirk at Bob Dylan because the times don’t really change? Would one do a cost/benefit analysis of caring for one’s child?

… since God and belief in God are human preoccupations based upon faith, they are not subject to rationalist/empiricist argumentation. You may call it “irrational” but I might propose calling it “hyper-rational.””

The idea here is that there are matters that are not subject to reason and evidence and that the question of God's existence is one of those matters.

If true, then one's belief in God simply cannot be questioned or challenged. This is a big & bold claim that serves to insulate one's belief from criticism.

Sweet.

But imagine the defendant in a murder trial asserting that there are matters not subject to reason and evidence and that the question of his guilt is one of those matters. The incoming tide of further accusations he would face from judge, jury, and the wider court of public opinion would surely include arrogance, stupidity, & foolishness. I mean, it'd be a great move if one could pull it, but can one really ever pull it? What exactly are these matters that are not subject to reason and evidence, and is the question of God's existence really one of them?

Consider a couple of questions. Do reason and evidence explain why we fall in love with whom we do? Can reason and evidence explain why I don't like anchovies? Emotional matters and personal tastes cannot (yet!) be satisfactorily explained by reason and evidence, but it would be absurd to suggest that questions about the existence or nonexistence of certain entities (or the guilt or innocence of those charged) can be answered using emotions and personal preferences, wouldn't it? Would you believe in the existence of Bigfoot on the basis of emotions or personal preferences?

What I think is lurking behind the comments I quoted is that God is supernatural. That's relevant because it is widely believed that the supernatural is a matter that, perhaps forever (but at least for the moment), lies beyond (and is therefore not subject to) reason and evidence. The supernatural is "hyper-rational". Not surprisingly, I have heard similar claims made by people defending alternative medical treatments. Here's what a friend of mine had to say about the paucity of high quality evidence supporting acupuncture and the wealth of evidence indicating that it's nothing more than the power of suggestion :

" in the chaos of nature, there is more that we don't understand than do, and it is arrogant to think that controlled experiments in hermetically sealed labs can in any way replicate the chaos and uncertainty that occurs in nature."

Ahh, yes. I've heard that first part before, somewhere ...

"There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy." - Shakespeare, Hamlet

My advice to you? Beware when you encounter this quote. The person using it is probably feeling that their belief is under some significant pressure and the best way to relieve it is to suggest that it's beyond Earth, Heaven, and even reason itself. You can be sure that if reason and evidence were available to establish their belief, you'd be hearing all about it (this is known as apologetics), but when the belief persists in the face of insufficient reason and evidence (the definition of faith?), then this old canard may make an appearance in the conversation. And notice that it is a conversation stopper:

"I'm talking about something that's beyond you, beyond everything, and neither you nor anybody can touch it."

This attitude - that one is in possession of information that transcends reason and empirical evidence - can be harmless, but it can also lead people to accept ineffective treatments when effective ones exist (see here and here), and it lies behind religiously motivated discrimination and slaughter of infidels and perpetrators of imaginary crimes- the most horrible and tragic aspects of faith-based beliefs.

So this important question still stands: Is the supernatural off-limits for reason and evidence? Chime in and let me know what you think. I'll be responding in a few days.

A message for my children

Richard Dawkins wrote this letter to his daughter. I'd like to share it with my children when they are of age. It's not a full treatise on epistemology -Dawkins isn't a philosopher - but it gets a message he and I hold dear nicely across. I wouldn't change a word.

"To my dearest daughter,

Now that you are ten, I want to write to you about something that is important to me. Have you ever wondered how we know the things that we know? How do we know, for instance, that the stars, which look like tiny pinpricks in the sky, are really huge balls of fire like the Sun and very far away? And how do we know that the Earth is a smaller ball whirling round one of those stars, the Sun?

The answer to these questions is ‘evidence’.

Sometimes evidence means actually seeing (or hearing, feeling, smelling….) that something is true. Astronauts have traveled far enough from the Earth to see with their own eyes that it is round. Sometimes our eyes need help. The ‘evening star’ looks like a bright twinkle in the sky but with a telescope you can see that it is a beautiful ball – the planet we call Venus. Something that you learn by direct seeing (or hearing or feeling…) is called an observation. Often evidence isn’t just observation on its own, but observation always lies at the back of it. If there’s been a murder, often nobody (except the murderer and the dead person!) actually observed it. But detectives can gather together lots of other observations which may all point towards a particular suspect. If a person’s fingerprints match those found on a dagger, this is evidence that he touched it. It doesn’t prove that he did the murder, but it can help when it’s joined up with lots of other evidence. Sometimes a detective can think about a whole lot of observations and suddenly realize that they all fall into place and make sense if so-and-so did the murder.

Scientists – the specialists in discovering what is true about the world and the universe – often work like detectives. They make a guess (called a hypothesis) about what might be true. They then say to themselves: if that were really true, we ought to see so-and-so. This is called a prediction. For example, if the world is really round, we can predict that a traveler, going on and on in the same direction, should eventually find himself back where he started. When a doctor says that you have measles he doesn’t take one look at you and see measles. His first look gives him a hypothesis that you may have measles. Then he says to himself: if she really has measles, I ought to see… Then he runs through his list of predictions and tests them with his eyes (have you got spots?), his hands (is your forehead hot?), and his ears (does your chest wheeze in a measly way?). Only then does he make his decision and say, ‘I diagnose that the child has measles.’ Sometimes doctors need to do other tests like blood tests or X-rays, which help their eyes, hands and ears to make observations.

The way scientists use evidence to learn about the world is much cleverer and more complicated than I can say in a short letter. But now I want to move on from evidence, which is a good reason for believing something, and warn you against three bad reasons for believing anything. They are called ‘tradition’, ‘authority’, and ‘revelation’.

First, tradition. A few months ago, I went on television to have a discussion with about 50 children. These children were invited because they’d been brought up in lots of different religions. Some had been brought up as Christians, others as Jews, Muslims, Hindus, Sikhs. The man with the microphone went from child to child, asking them what they believed. What they said shows up exactly what I mean by ‘tradition’. Their beliefs turned out to have no connection with evidence. They just trotted out the beliefs of their parents and grandparents, which, in turn, were not based upon evidence either. They said things like, ‘We Hindus believe so and so.’ ‘We Muslims believe such and such.’ ‘We Christians believe something else.’ Of course, since they all believed different things, they couldn’t all be right. The man with the microphone seemed to think this quite proper, and he didn’t even try to get them to argue out their differences with each other. But that isn’t the point I want to make. I simply want to ask where their beliefs came from. They came from tradition. Tradition means beliefs handed down from grandparent to parent to child, and so on. Or from books handed down through the centuries. Traditional beliefs often start from almost nothing; perhaps somebody just makes them up originally, like the stories about Thor and Zeus. But after they’ve been handed down over some centuries, the mere fact that they are so old makes them seem special. People believe things simply because people have believed the same thing over centuries. That’s tradition.

The trouble with tradition is that, no matter how long ago a story was made up, it is still exactly as true or untrue as the original story was. If you make up a story that isn’t true, handing it down over any number of centuries doesn’t make it any truer!

Most people in England have been baptized into the Church of England, but this is only one of many branches of the Christian religion. There are other branches such as the Russian Orthodox, the Roman Catholic and the Methodist churches. They all believe different things. The Jewish religion and the Muslim religion are a bit more different still; and there are different kinds of Jews and of Muslims. People who believe even slightly different things from each other often go to war over their disagreements. So you might think that they must have some pretty good reasons – evidence – for believing what they believe. But actually their different beliefs are entirely due to different traditions.

Let’s talk about one particular tradition. Roman Catholics believe that Mary, the mother of Jesus, was so special that she didn’t die but was lifted bodily into Heaven. Other Christian traditions disagree, saying that Mary did die like anybody else. These other religions don’t talk about her much and, unlike Roman Catholics, they don’t call her the ‘Queen of Heaven’. The tradition that Mary’s body was lifted into Heaven is not a very old one. The Bible says nothing about how or when she died; in fact the poor woman is scarcely mentioned in the Bible at all. The belief that her body was lifted into Heaven wasn’t invented until about six centuries after Jesus’s time. At first it was just made up, in the same way as any story like Snow White was made up. But, over the centuries, it grew into a tradition and people started to take it seriously simply because the story had been handed down over so many generations. The older the tradition became, the more people took it seriously. It finally was written down as an official Roman Catholic belief only very recently, in 1950. But the story was no more true in 1950 than it was when it was first invented 600 years after Mary’s death.

I’ll come back to tradition at the end of my letter, and look at it in another way. But first I must deal with the two other bad reasons for believing in anything: authority and revelation. Authority, as a reason for believing something, means believing it because you are told to believe it by somebody important. In the Roman Catholic Church, the Pope is the most important person, and people believe he must be right just because he is the Pope. In one branch of the Muslim religion, the important people are old men with beards called Ayatollahs. Lots of young Muslims are prepared to commit murder, purely because the Ayatollahs in a faraway country tell them to.

When I say that it was only in 1950 that Roman Catholics were finally told that they had to believe that Mary’s body shot off to Heaven, what I mean is that in 1950 the Pope told people that they had to believe it. That was it. The Pope said it was true, so it had to be true! Now, probably some of the things that Pope said in his life were true and some were not true. There is no good reason why, just because he was the Pope, you should believe everything he said, any more than you believe everything that lots of other people say. The present Pope has ordered his followers not to limit the number of babies they have. If people follow his authority as slavishly as he would wish, the results could be terrible famines, diseases and wars, caused by overcrowding.

Of course, even in science, sometimes we haven’t seen the evidence ourselves and we have to take somebody else’s word for it. I haven’t with my own eyes, seen the evidence that light travels at a speed of 186,000 miles per second. Instead, I believe books that tell me the speed of light. This looks like ‘authority’. But actually it is much better than authority because the people who wrote the books have seen the evidence and anyone is free to look carefully at the evidence whenever they want. That is very comforting. But not even the priests claim that there is any evidence for their story about Mary’s body zooming off to Heaven.

The third kind of bad reason for believing anything is called ‘revelation’. If you had asked the Pope in 1950 how he knew that Mary’s body disappeared into Heaven, he would probably have said that it had been ‘revealed’ to him. He shut himself in his room and prayed for guidance. He thought and thought, all by himself, and he became more and more sure inside himself. When religious people just have a feeling inside themselves that something must be true, even though there is no evidence that it is true, they call their feeling ‘revelation’. It isn’t only popes who claim to have revelations. Lots of religious people do. It is one of their main reasons for believing the things that they do believe. But is it a good reason?

Suppose I told you that your dog was dead. You’d be very upset, and you’d probably say, ‘Are you sure? How do you know? How did it happen?’ Now suppose I answered: ‘I don’t actually know that Pepe is dead. I have no evidence. I just have this funny feeling deep inside me that he is dead.’ You’d be pretty cross with me for scaring you, because you’d know that an inside ‘feeling’ on its own is not a good reason for believing that a whippet is dead. You need evidence. We all have inside feelings from time to time, and sometimes they turn out to be right and sometimes they don’t. Anyway, different people have opposite feelings, so how are we to decide whose feeling is right? The only way to be sure that a dog is dead is to see him dead, or hear that his heart has stopped; or be told by somebody who has seen or heard some real evidence that he is dead.

People sometimes say that you must believe in feelings deep inside, otherwise you’d never be confident of things like ‘My wife loves me’. 

But this is a bad argument. There can be plenty of evidence that somebody loves you. All through the day when you are with somebody who loves you, you see and hear lots of little tidbits of evidence, and they all add up. It isn’t purely inside feeling, like the feeling that priests call revelation. There are outside things to back up the inside feeling: looks in the eye, tender notes in the voice, little favors and kindnesses; this is all real evidence.

Sometimes people have a strong inside feeling that somebody loves them when it is not based upon any evidence, and then they are likely to be completely wrong. There are people with a strong inside feeling that a famous film star loves them, when really the film star hasn’t even met them. People like that are ill in their minds. Inside feelings must be backed up by evidence, otherwise you just can’t trust them.

Inside feelings are valuable in science too, but only for giving you ideas that you later test by looking for evidence. A scientist can have a ‘hunch’ about an idea that just ‘feels’ right. In itself, this is not a good reason for believing something. But it can be a good reason for spending some time doing a particular experiment, or looking in a particular way for evidence. Scientists use inside feelings all the time to get ideas. But they are not worth anything until they are supported by evidence.

I promised that I’d come back to tradition, and look at it in another way. I want to try to explain why tradition is so important to us. All animals are built (by the process called evolution) to survive in the normal place in which their kind live. Lions are built to be good at surviving on the plains of Africa. Crayfish are built to be good at surviving in fresh water, while lobsters are built to be good at surviving in the salt sea. People are animals too, and we are built to be good at surviving in a world full of … other people. Most of us don’t hunt for our own food like lions or lobsters, we buy it from other people who have bought it from yet other people. We ‘swim’ through a ‘sea of people’. Just as a fish needs gills to survive in water, people need brains that make them able to deal with other people. Just as the sea is full of salt water, the sea of people is full of difficult things to learn. Like language.

You speak English but your friend speaks German. You each speak the language that fits you to ‘swim about’ in your own separate ‘people sea’. Language is passed down by tradition. There is no other way. In England, Pepe is a dog. In Germany he is ein Hund. Neither of these words is more correct, or more truer than the other. Both are simply handed down. In order to be good at ‘swimming about in their people sea’, children have to learn the language of their own country, and lots of other things about their own people; and this means that they have to absorb, like blotting paper, an enormous amount of traditional information. (Remember that traditional information just means things that are handed down from grandparents to parents to children.) The child’s brain has to be a sucker for traditional information. And the child can’t be expected to sort out good and useful traditional information, like the words of a language, from bad or silly traditional information, like believing in witches and devils and ever-living virgins.

It’s a pity, but it can’t help being the case, that because children have to be suckers for traditional information, they are likely to believe anything the grown-ups tell them, whether true or false, right or wrong. Lots of what grown-ups tell them is true and based on evidence or at least sensible. But if some of it is false, silly or even wicked, there is nothing to stop the children believing that too. Now, when the children grow up, what do they do? Well, of course, they tell it to the next generation of children. So, once something gets itself strongly believed – even if its completely untrue and there never was any reason to believe it in the first place – it can go on forever.

Could this be what happened with religions? Belief that there is a god or gods, belief in Heaven, belief that Mary never died, belief that Jesus never had a human father, belief that prayers are answered, belief that wine turns into blood – not one of these beliefs is backed up by any good evidence. Yet millions of people believe them. Perhaps this is because they were told to believe them when they were young enough to believe anything.

Millions of other people believe quite different things, because they were told different things when they were children. Muslim children are told different things from Christian children, and both grow up utterly convinced that they are right and the others are wrong. Even within Christians, Roman Catholics believe different things from Church of England people or Episcopalians, Shakers or Quakers, Mormons or Holy Rollers, and all are utterly convinced that they are right and the others are wrong. They believe different things for exactly the same kind of reason as you speak English and someone speaks German. Both languages are, in their own country, the right language to speak. But it can’t be true that different religions are right in their own countries, because different religions claim that opposite things are true. Mary can’t be alive in the Catholic Republic but dead in Protestant Northern Ireland.

What can we do about all this? It is not easy for you to do anything, because you are only ten. But you could try this. 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.

Your loving,

Daddy"