“Certainty? In this world nothing is certain but death and taxes.” – Benjamin Franklin

“What men really want is not knowledge but certainty.” – Bertrand Russell

“The quest for certainty blocks the search for meaning. Uncertainty is the very condition to impel man to unfold his powers.” – Erich Fromm

“Doubt is not a pleasant condition, but certainty is absurd.” – Voltaire

“Fear comes from uncertainty. When we are absolutely certain, whether of our worth or worthlessness, we are almost impervious to fear.” – William Congreve

Let me add my own quotable quote concerning certainty: The certainty that one is correct is the most reliable predictor of error, for knowledge stems from scientific methodology and certainty is anathema to such inquiry.

Recently I wrote about the general methodological differences between skeptics and believers. I did not touch upon the notion of certainty, but this is an absolutely critical distinction, and is a common theme behind many pseudoscientific beliefs. A good scientific skeptic must learn to be comfortable with doubt. In fact the very process of skepticism begins and ends with doubt. The methods of good scientific investigation stem from systematically doubting everything we think we know and every step in a chain of evidence or argument. Scientists know that all conclusions in science are tentative – that is just another way of talking about the central role of doubt and uncertainty in science.

The problem with being certain is that it fixes our conclusions. If we know deep in our soul that something is right, then no evidence or logic can knock that belief from its pedestal. We are then forced to work backwards – to start with the certain conclusion and then cherry pick and shoehorn in the evidence to prove what we already “know” to be true. This is the defining methodological characteristic of pseudoscience.

We see this process at work in conspiracy thinking. I have recently had numerous exchanges with those who support some variation of the belief that the US government was involved with the terrorist attacks on 9/11. Typically conspiracy theorists suffer from a surfeit of certitude, which makes them both arrogant and wrong. It also makes them feel as if everyone who does not see the conspiracy is naïve. They believe that they truly see the dark hand of a sinister conspiracy at work behind the scenes. They have seen or heard too many things that just don’t make sense any other way, or seem to confirm that there is a conspiracy. Eventually they get to the point that they are certain there is a conspiracy – there is just no other way for them to make sense of all the apparent anomalies. The conspiracy makes sense of it all, it comforts them with an explanatory model that accommodates all the evidence.

It also reveals another consequence of certainty – it leads to the insulation of the belief. If we are certain that something is true then we must protect the conclusion from falsification. So we meet challenges to the conclusion with special pleading, with denial, with ad hominem dismissals, with whatever it takes. We know our conclusion is true, so anything that calls the conclusion into question must be false.

What conspiracy theorists fail to do is what any good skeptic should do – step back and ask the big question: can I be wrong about this? What if there were no conspiracy on 9/11, what if the official version of events is true? Is this compatible with all the evidence?

There have been a number of recent blog exchanges concerning the “mercury militia” – a grassroots organization of people who believe that mercury, and specifically mercury in vaccines, causes autism and a host of other medical problems. The mercury proponents are often characterized as militant because they have used bullying tactics to push their agenda. The extremity of their methods stems from the certainty of their conclusions. They are not trying to investigate with the scientific community what the cause(s) of autism is, or what the health effects of mercury are. Rather, they are certain mercury causes autism, so everyone who also thinks this is their ally, and everyone who doubts this conclusion is their enemy.

There are various reasons for their certainty, but in my experience I think that most are honestly convinced by the scientific evidence. Mercury is, in fact, a neurotoxin. If you put mercury into a Petri dish with brain cells, really bad things happen to the brain cells. The mercury militia have seen this evidence, and they have taken from it a certitude that mercury caused their child’s autism. And of course, that was their fatal mistake – the certitude. It turns out that the dose of mercury from vaccines in a living person is not sufficient to cause autism or any other neurological disorder (probably), and epidemiological studies have failed to show any correlation between vaccines and autism. It also turns out that there is compelling evidence for a genetic cause or causes of autism – even though we are far away from a full understanding of this disorder.

But none of this matters – the mercury believers locked in their conclusions and further evidence is irrelevant.

Two years ago I wrote a rather extensive article on this issue, and spent about 6 months doing background research before I wrote it. I went into the project with the strong suspicion that there was no connection between vaccines and autism, from what I had already read. But when I was in the middle of the research, and had seen much of the biological evidence for the toxicity of mercury, I did step back and ask the big question. Is there a possible connection here? My article would have been much more interesting and provocative if I came to the conclusion that there was, but my only concern was getting it right. Eventually I concluded that there is no connection – the evidence is actually quite clear at this point. But as always I remain open to further evidence.

Many of the mercury proponents were convinced by the same kind of evidence that compels many to accept some form of alternative medicine or even any paranormal belief – a compelling anecdote. People are highly persuaded by personal stories. If you are a parent of a child with autism and another parent tells you that their autistic child was cured by chelation therapy (a treatment that removes mercury) – that is damn convincing. I once asked a naturopath how they could believe in homeopathy and their response was, “Because I have seen it work in my practice.”

The most compelling anecdotal evidence is our own experience. There is no shorter pathway to certainty than personal experience. If you see a ghost for yourself, then all the logical arguments in the world are unlikely to dissuade you from your belief in ghosts.

It makes sense that we would put great stock in our own experience, and it is the hardest thing to do to say that you can be profoundly wrong about something that you are very sure of. It is unsettling to think that our memories are fallible, our senses unreliable, that our emotions reign over our intellect, and our conclusions can be so uncertain. We also attach a certain amount of pride to being right, and shame to being wrong.

The solution is to adopt the sensibilities of a skeptic. Skeptics, like good scientists, do not stake their reputation or their ego on being correct – they stake it in using good methodology, on being honest, and on being fair. It is therefore OK to be wrong. If in the future evidence comes to light that adequately demonstrates vaccines do cause autism, I will happily revise my conclusions. This is because my reputation as an intellectual and a skeptic is more dependent upon my adapting my tentative conclusions to new evidence, rather than being correct in the past. All I can say is that I came to the best conclusion given the evidence available at the time.

This means living in a world of doubt. But doubt is good, because it forces us to question, to listen to the evidence, to change in response to compelling evidence, and to be open. Certainty forces us to dismiss evidence, to insulate our beliefs, to use bad logic, to become arrogant and closed-minded, and even militant. There is no limit to the atrocities that can be committed in the name of certainty. The pilots who crashed commercial jets into three buildings on 9/11 were probably certain of their moral correctness. They probably did not step back and ask the big question – can I be wrong about this?

But of course, I could be wrong.