pertain vs touch on

pertain

verb
  • To relate, to refer, be relevant to. 

  • To apply; to be or remain in place; to continue to be applicable. 

  • To belong to or be a part of; be an adjunct, attribute, or accessory of. 

touch on

verb
  • To mention briefly; to cursorily discuss. 

  • To come or go to for a short time. 

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