postulator vs affirmer

postulator and affirmer both are nouns.

Word	Noun	Adjective	Verb	Adverb
postulator	Yes	No	No	No
affirmer	Yes	No	No	No

As nouns, affirmer is a hypernym of postulator; that is, affirmer is a word with a broader meaning than postulator:

postulator: someone who assumes or takes something for granted as the basis of an argument
affirmer: someone who claims to speak the truth

Other hypernyms of postulator include asserter, asseverator, avower, declarer.

postulator (noun)	affirmer (noun)
someone who assumes or takes something for granted as the basis of an argument	someone who claims to speak the truth
(Roman Catholic Church) someone who proposes or pleads for a candidate for beatification or canonization