bring to heel vs soften

bring to heel

verb
  • To cause to act in a disciplined manner. 

  • To compel someone to obey; to force someone into a submissive condition. 

soften

verb
  • To undermine the morale of someone (often soften up). 

  • To make something soft or softer. 

  • To palatalize. 

  • To become or make (a consonant) more lenis, to lenite. 

  • To make less harsh 

  • To become soft or softer 

How often have the words bring to heel and soften occurred in a corpus of books? (source: Google Ngram Viewer )