formulate vs play by ear

formulate

verb
  • To put into a clear and definite form of statement or expression. 

play by ear

verb
  • To do by guessing, intuition, or trial and error; to react to events as they occur; improvise 

  • To play guided by one's musical ear, rather than from a written score. 

How often have the words formulate and play by ear occurred in a corpus of books? (source: Google Ngram Viewer )