aio

aio is defective: it lives in the present and imperfect and nowhere much else. There is no perfect and no infinitive in ordinary use, so where you need one, Latin borrows from dico. The forms you will actually meet are ait, "he says" or "he said", and aiunt, "they say"; then aio, ais, and the imperfect aiebat, aiebant.

It is the verb for reporting a claim, and it takes an accusative and infinitive: ait se venturum esse. The parenthetical inquit, also defective, does the neighbouring job of framing DIRECT speech, so a quotation gets inquit and a report gets ait. The oracle's famous double-edged reply to Pyrrhus, aio te, Aeacida, Romanos vincere posse, turns entirely on that accusative-and-infinitive: it can be read as "you can beat the Romans" or "the Romans can beat you".