The Collaborative International Dictionary of English v.0.48:
assertable \assertable\ adj. 1. capable of being affirmed or asserted. Syn: affirmable. [WordNet 1.5]WordNet (r) 3.0 (2006):
assertable adj 1: capable of being affirmed or asserted; "a quality affirmable of every member of the family" [syn: affirmable, assertable]