free speech vs freedom of speech

free speech

noun
  • The right to express an opinion in public without being restrained or censored. 

  • Expressions that are or should be allowed in some moral or legal context. 

freedom of speech

noun
  • The right of citizens to speak, or otherwise communicate, without fear of harm or prosecution. 

  • Used other than figuratively or idiomatically: see freedom, speech. 

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