commend vs pat on the back

commend

verb
  • To congratulate or reward. 

  • To recommend. 

  • To entrust or commit to the care of someone else. 

  • To praise or acclaim. 

  • To mention by way of courtesy, implying remembrance and goodwill. 

pat on the back

verb
  • To praise or congratulate. 

noun
  • Praise, congratulations. 

How often have the words commend and pat on the back occurred in a corpus of books? (source: Google Ngram Viewer )