fire-breathing dragon lives in my garage’ Suppose I seriously make such an assertion to you. Surely you’d want to check it out, see for yourself. There have been innumerable stories of dragons over the centuries, but no real evidence. What an opportunity! ‘Show me,’ you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle – but no dragon. ‘Where’s the dragon?’ you ask. ‘Oh, she’s right here,’ I reply, waving vaguely. ‘I neglected to mention that she’s an invisible

