Fake news, how do you know that as a fact? Well somebody else 'knows' so it must be a fact

POST-TRUTH was 2016’s word of the year, according to Oxford Dictionaries. Not least in the furious debates surrounding the UK Brexit vote and Donald Trump’s 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’s all a storm in a teacup – there’s no such thing as objective truth that exists outside our minds. Nonsense, harrumphs Peter van Inwagen of the University of Notre Dame in Indiana. If a doctor says I have cancer of the gut, he says, “whether that is true depends on what is going on in my gut, and not on what is going on in my doctor’s mind”. Accept that, and the challenge – in the post-truth era as much as in the pre-post-truth era – is to ensure that our inside knowledge is aligned as far as possible with outside truth. That’s hard, not least because in a complex society we rely on the knowledge of others, even when we don’t realise it. Ask someone if they know how an everyday object such as a ballpoint pen works and they’ll 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 Source New Scientist