In a world obsessed with Trump, alternative facts have not had a great press. But it is a century and more since Nietzsche claimed 'there are no facts, only interpretations' - and fifty years since Thomas Kuhn argued that facts were theory dependent. Is an insistence on 'the facts' the dogmatic prejudice of believers in their particular truth? Do we have to give up the idea that facts decide the matter? Or are facts essential to science and progress, and without them only chaos reigns?