enforced vs voluntary

enforced

voluntary

noun
  • A supporter of voluntarism; a voluntarist. 

  • A short piece of music, often having improvisation, played on a solo instrument. 

  • A volunteer. 

adj
  • Done, given, or acting of one's own free will. 

  • Done by design or intention; intentional. 

  • Of or relating to voluntarism. 

  • Endowed with the power of willing. 

  • Working or done without payment. 

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