an

An is the "or" of QUESTIONS and only of questions. For "or" in a statement Latin uses aut, where the alternatives exclude each other, or vel, where either will do. An offers an alternative inside a question, direct or indirect, and nowhere else.

In a double question the first limb is usually marked, by utrum or by the enclitic -ne, and an introduces the second: utrum manes an abis. In an indirect question after verbs of asking, doubting and not knowing it is simply "whether".

The one idiom that catches everybody is haud scio an, and its twin nescio an. These look like "I do not know whether" and mean the opposite: they are a polite way of asserting something, "I rather think, I am inclined to believe". Haud scio an verum dicat is a mild yes, not a shrug. Annon is the negative pair, "or not".