ergo vs therefor

ergo

adv
  • Consequently, therefore, or thus. 

noun
  • An ergonomic factor or characteristic. 

conj
  • therefore (especially in syllogisms) 

therefor

adv
  • For that; in return for that. 

  • Coordinate terms: herefor, wherefor 

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