Imagination is often used for play, but Timothy Williamson reminds us that imagination is critical for serious thinking:

[I]magination is not only about fiction: it is integral to our painful progress in separating fiction from fact. Although fiction is a playful use of imagination, not all uses of imagination are playful. Like a cat’s play with a mouse, fiction may both emerge as a by-product of un-playful uses and hone one’s skills for them.