keep on vs remain

keep on

verb
  • To persist or continue. 

  • To cause or allow to remain in the on or open position. 

  • To cause or allow to remain in an existing position. 

  • To persist in talking about a subject to the annoyance of the listener. 

remain

verb
  • To continue in a state of being. 

  • To await; to be left to. 

  • To continue unchanged in place, form, or condition, or undiminished in quantity; to abide; to stay; to endure; to last. 

  • To be left after a number or quantity has been subtracted or cut off; to be left as not included or comprised. 

  • To stay after others or other parts have been removed or otherwise disappeared. 

noun
  • That which is left; relic; remainder. 

  • That which is left of a human being after the life is gone; relics; a dead body. 

  • Posthumous works or productions, especially literary works. 

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