Dic: Synonyms: confirm, corroborate, substantiate, authenticate, validate, verify

These verbs mean to affirm the truth, accuracy, or genuineness of something.

• Confirm implies removal of all doubt:
  .... "We must never make experiments to confirm our ideas, but simply to control them" (Claude Bernard). 
• Corroborate refers to supporting something by means of strengthening evidence:
  .... The witness is expected to corroborate the plaintiff's testimony. 
• To substantiate is to establish by presenting substantial or tangible evidence:
  .... "one of the most fully substantiated of historical facts" (James Harvey Robinson). 
• Authenticate implies the establishment of genuineness of something by the testimony of an expert:
  .... Never purchase an antique before it has been authenticated. 
• Validate refers to establishing the validity of something, such as a theory, claim, or judgment:
  .... The divorce validated my parents' original objection to the marriage. 
• Verify implies proving by comparison with an original or with established fact:
  .... The bank refused to cash the check until the signature was verified.

... The American Heritage, http://www.thefreedictionary.com/confirm