maxim vs motto

maxim

noun
  • A precept; a succinct statement or observation of a rule of conduct or moral teaching. 

motto

noun
  • A sentence, phrase, or word, prefixed to an essay, discourse, chapter, canto, or the like, suggestive of its subject matter; a short, suggestive expression of a guiding principle; a maxim. 

  • A sentence, phrase, or word, forming part of an heraldic achievement. 

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