digression vs modification

digression

noun
  • The act of straying from the main subject in speech or writing, (rhetoric) particularly for rhetorical effect. 

  • An aside, an act of straying from the main subject in speech or writing. 

  • An elongation, a deflection or deviation from a mean position or expected path. 

modification

noun
  • The act of making a change to something while keeping its essential character intact; an alteration or adjustment. 

  • A change to an organism as a result of its environment that is not transmissable to offspring. 

  • the change undergone by a word when used in a construction (for instance am => 'm in I'm) 

  • a change to a word when it is borrowed by another language 

  • The result of modifying something; a new or changed form. 

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