impossibility vs occasion

impossibility

noun
  • Something that is impossible. 

  • The quality of being impossible. 

occasion

noun
  • Something which causes something else; a cause. 

  • Need; requirement, necessity. 

  • The time when something happens. 

  • A reason or excuse; a motive; a persuasion. 

  • A special event or function. 

  • A particular happening; an instance or time when something occurred. 

  • An occurrence or state of affairs which causes some event or reaction; a motive or reason. 

  • A favorable opportunity; a convenient or timely chance. 

verb
  • To cause; to produce; to induce 

How often have the words impossibility and occasion occurred in a corpus of books? (source: Google Ngram Viewer )