affirm vs vouch

affirm and vouch both are verbs.

Word	Noun	Adjective	Verb	Adverb
affirm	No	No	Yes	No
vouch	No	No	Yes	No

As verbs, vouch is a hyponym of affirm; that is, vouch is a word with a more specific, narrower meaning than affirm:

Other hyponyms of affirm include back, back up, verify, demonstrate, establish, prove, shew, show, document, validate.

affirm (verb)	vouch (verb)
establish or strengthen as with new evidence or facts	give supporting evidence
to declare or affirm solemnly and formally as true	summon (a vouchee) into court to warrant or defend a title
say yes to	give personal assurance; guarantee
	give surety or assume responsibility