affirm vs substantiate

affirm and substantiate both are verbs.

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

As verbs, affirm and substantiate are synonyms defined as:

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

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

affirm (verb)	substantiate (verb)
establish or strengthen as with new evidence or facts	solidify, firm, or strengthen
to declare or affirm solemnly and formally as true	establish or strengthen as with new evidence or facts
say yes to	make real or concrete; give reality or substance to
	represent in bodily form