So, when a child is saying ‘let’s pretend’, what they’re really saying is ‘let’s imagine’. Imagining is possibly the central human trick. That’s what distinguishes us from all other creatures.

We know from quite careful study now that the amount that other animals can imagine is very, very limited compared to ours. We can imagine worlds that don’t exist. We can not only imagine them, we can imagine what is going on within them. We can change details, we can say ‘okay, I’ll make it this instead of that and then see what happens’. So we can play out whole scenarios in our head in imagination. And that, of course, makes us able to experience empathy, for example. By definition, empathy is having the feeling of what the world is like in somebody else’s head. Well you can only do that, really, if you are skilled at this job of world-building.