inform vs keep someone posted

inform

verb
  • To communicate knowledge to. 

  • To give form or character to; to inspire (with a given quality); to affect, influence (with a pervading principle, idea etc.). 

  • To act as an informer; denounce. 

  • To impart information or knowledge. 

adj
  • Without regular form; shapeless; ugly; deformed. 

keep someone posted

verb
  • To inform (someone) regularly of the latest developments. 

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