POST-TRUTH was 2016鈥檚 word of the year, according to Oxford Dictionaries. Not least in the furious debates surrounding the UK Brexit vote and Donald Trump鈥檚 election as US president, claims and counter claims of fake news, dodgy experts and media mendacity have been flying around.
For a hardcore of relativist philosophers, that鈥檚 all a storm in a teacup 鈥� there鈥檚 no such thing as objective truth that exists outside our minds. Nonsense, harrumphs of the University of Notre Dame in Indiana. If a doctor says I have cancer of the gut, he says, 鈥渨hether that is true depends on what is going on in my gut, and not on what is going on in my doctor鈥檚 mind鈥�.
Inside knowledge: The biggest questions about facts, truth, lies and belief
Forget alternative facts. To get to the bottom of what we know and how we know we know it, delve into our special report on epistemology 鈥� the science of knowledge itself
Accept that, and the challenge 鈥� in the post-truth era as much as in the pre-post-truth era 鈥� is to ensure that our inside knowledge is aligned as far as possible with outside truth.
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That鈥檚 hard, not least because in a complex society we rely on the knowledge of others, even when we don鈥檛 realise it. Ask someone if they know how an everyday object such as a ballpoint pen works and they鈥檒l generally say yes, until you ask them to explain it. It turns out that our confidence in our own knowledge is often based on the certainty that somebody else knows.
That is often good enough; ballpoint pens exist and work. 鈥淎s individuals we know hardly anything,鈥� says of Brown University in Providence, Rhode Island, co-author of The Knowledge Illusion: Why we never think alone. 鈥淏ut most of us do very well and as a society we create incredible things. We sent a person to the moon. How is that all possible? Because of the knowledge of other people.鈥�
So how much should we trust people who actually do know stuff? 鈥淚t鈥檚 not that we want people to uncritically accept whatever experts say,鈥� says Timothy Williamson of the University of Oxford. A certain level of scepticism is healthy.
鈥淚f you are a sceptic, you won鈥檛 be convinced by conspiracy theories鈥�
But it makes things difficult if we begin to mistrust expertise as a default. In philosophy, a true sceptic questions everything, so they have nothing left to build knowledge on. That鈥檚 where we don鈥檛 want to go as a society 鈥� while not losing sight of the fact that expertise differs in value and reliability (see 鈥�Felicitous falsehoods鈥�). We should accept that, if we need a tooth pulled, going to see someone with a degree in dentistry just guarantees a dentist, not necessarily a good dentist, says of Harvard University.
How do we tread that fine line between healthy scepticism and destructive cynicism? First, think critically and assess the credentials, track record and potential bias of the sources we rely on. 鈥淚f somebody is telling me this, what motives could that person have for wanting me to believe that, other than that it鈥檚 true?鈥� says van Inwagen. 鈥淭hose are the practical questions.鈥�
Pose the same questions of yourself, too. 鈥淎sk 鈥楬ow do you know?鈥�, 鈥楬ow do they know?鈥�, all the time,鈥� says Elgin. Train yourself to ask whether your reaction to new knowledge is rooted in something trustworthy or something else, like wishful thinking. 鈥淭hink about something like global warming,鈥� says Elgin. 鈥淭o do something about that might require a certain amount of rather inconvenient stuff, so you鈥檇 really rather not believe it and start to make the sacrifices you would have to make.鈥�
And finally, avoid the seductive belief that you are privy to knowledge purposely being denied to others, or a warrior for truth when all others are peddling lies. Human beings are, in general, terrible at keeping secrets. 鈥淚f you were sceptical you wouldn鈥檛 be convinced by conspiracy theories,鈥� says van Inwagen. But these experts would say that, wouldn鈥檛 they?
Felicitous falsehoods
To get at the truth, sometimes we need to lie 鈥� for instance in building up scientific models that simplify an often complex world. The ideal gas law, for example, tells us how the volume, pressure and temperature of a gas are related, but assumes the individual molecules of the gas behave as perfect spheres that bounce off each other elastically.
Of course they don鈥檛. 鈥淏ut if you took into account the actual shapes of the actual gas molecules in a volume of gas, just the geometry, the problem of saying what is going on with this gas, would be incalculable,鈥� says Catherine Elgin, a philosopher at Harvard University.
So these felicitous falsehoods help us dig at deeper truths 鈥� as long as we don鈥檛 forget where they are and let them become the weight-bearing part of the structures we build.
Economists, for example, have traditionally created models of stable markets by assuming that buyers and sellers have perfect information and make rational choices 鈥� only to be constantly surprised when the irrationality of human decision-making creates a messier reality.
So simplify for science鈥檚 sake 鈥� but sensibly. 鈥淭he real problem isn鈥檛 with doing it, it鈥檚 not being aware of what you鈥檙e doing,鈥� says Elgin.
This article appeared in print under the headline 鈥淗ow can I know the truth?鈥�
