ergo vs thereby

ergo

adv
  • Consequently, therefore, or thus. 

noun
  • An ergonomic factor or characteristic. 

conj
  • therefore (especially in syllogisms) 

thereby

adv
  • By it; by that; by that means, or as a consequence of that. 

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