"Anyone inheriting the fantastic device of human language can say the green sun. Many can then imagine or picture it. But that is not enough--though it may already be a more potent thing than many a "thumbnail sketch" or "transcript of life" that receives literary praise.
"To make a Secondary World inside which the green sun will be credible, commanding Secondary Belief, will probably require labours and thought, and will certainly demand a special skill..."
(J. R. R. Tolkien "On Fairy-Stories")