Sentence:  Some who have written on Utopia have treated it as `` a learned diversion of a learned world '' , `` a phantasy with which More amused himself '' , `` a holiday work , a <WSD>spontaneous</WSD> overflow of intellectual high spirits , a revel of debate , paradox , comedy and invention '' . 
Meaning of the word marked with <WSD> tags:  happening or arising without apparent external cause