Synonyms for Incoherent (same or very similar meaning)
WordNet sense 1 (lacking orderly continuity):
confused, disconnected, illogical, unconnectedWordNet sense 2 (unable to express yourself clearly or fluently):
tongue-tiedWordNet sense 3 (without or deprived of the use of speech or words):
unarticulateFrom the ODE community, based on WordNetadd/edit