commentary vs discourse

commentary

noun
  • A series of comments or annotations; especially, a book of explanations or expositions on the whole or a part of some other work. 

  • An oral relation of an event, especially broadcast by television or radio, as it occurs. 

  • A brief account of transactions or events written hastily, as if for a memorandum. 

discourse

noun
  • A formal lengthy exposition of some subject, either spoken or written. 

  • Expression in words, either speech or writing. 

  • An institutionalized way of thinking, a social boundary defining what can be said about a specific topic (after Michel Foucault). 

  • Any rational expression, reason. 

verb
  • To exercise reason; to employ the mind in judging and inferring; to reason. 

  • To engage in discussion or conversation; to converse. 

  • To write or speak formally and at length. 

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