affirm vs demonstrate

affirm and demonstrate both are verbs.

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

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

affirm: establish or strengthen as with new evidence or facts
demonstrate: establish the validity of something, as by an example, explanation or experiment

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

affirm (verb)	demonstrate (verb)
establish or strengthen as with new evidence or facts	establish the validity of something, as by an example, explanation or experiment
to declare or affirm solemnly and formally as true	provide evidence for; stand as proof of; show by one's behavior, attitude, or external attributes
say yes to	give an exhibition of to an interested audience
	march in protest; take part in a demonstration