affirm vs sustain

affirm and sustain both are verbs.

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

As verbs, affirm and sustain are synonyms defined as:

affirm and sustain: establish or strengthen as with new evidence or facts

Other synonyms of affirm include confirm, corroborate, substantiate, support.

affirm (verb)	sustain (verb)
establish or strengthen as with new evidence or facts	undergo (as of injuries and illnesses)
to declare or affirm solemnly and formally as true	establish or strengthen as with new evidence or facts
say yes to	admit as valid
	supply with necessities and support
	provide with nourishment
	be the physical support of; carry the weight of
	lengthen or extend in duration or space