"[H]ow are mathematical activities like game-playing...? ...One makes sense of narrative, whether fictional or factual, by a mental construction that is sometimes called the world of story ...[which] may be the real world at some other time or right now in some other place, one sees that the imaginative effort is a standard way of understanding what people say... In order to understand connected speech about concrete things, one imagines them. This is as obvious as it is unclear how we do it. ...I imagine myself in those circumstances and ask myself what I can see. Pretending to be in those circumstances does not conflict with my certain knowledge that on the contrary I am listening to the news on my radio at home. The capacity to do this... encourages empathy, but it also allows one to do mathematics. ...This is often fun, and it is a form of playing with ideas."