compulsory law vs obligation

compulsory law

obligation

noun
  • A social, legal, or moral requirement, duty, contract, or promise that compels someone to follow or avoid a particular course of action. 

  • A course of action imposed by society, law, or conscience by which someone is bound or restricted. 

  • The act of binding oneself by a social, legal, or moral tie to someone. 

  • A legal agreement stipulating a specified action or forbearance by a party to the agreement; the document containing such agreement. 

  • The fact of being obliged to, that is, grateful for, something. 

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