impugn vs prove

impugn

verb
  • To verbally assault, especially to argue against an opinion, motive, or action; to question the truth or validity of. 

prove

verb
  • To ascertain or establish the genuineness or validity of; to verify. 

  • To demonstrate that something is true or viable; to give proof for. 

  • To put to the test, to make trial of. 

  • To determine by experiment which effects a substance causes when ingested. 

  • simple past tense of proove 

  • To turn out; to manifest. 

  • To turn out to be. 

noun
  • The process of dough proofing. 

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