talk about vs touch upon

talk about

verb
  • Used other than figuratively or idiomatically: see talk, about. (Compare discuss.) 

  • Used to draw attention to the speaker's approval or affirmation of someone or something 

  • Used to draw attention to the speaker's characterization of someone or something 

touch upon

How often have the words talk about and touch upon occurred in a corpus of books? (source: Google Ngram Viewer )