Instead of saying arn fíon, our wine, etc., the speakers of Irish found it easier to say arn víon. Instead of arn fuil, our blood, they said arn Wil. This new sound of v or W they represented by ḃ aspirated. Then, when the n of the eclipsing words dropped out, they began to write, as we do now, ar ḃfíon (veen), ar ḃfuil (Wil). Hence we say that f is eclipsed by ḃ aspirated.
§ 399. The particle an, used in asking questions, causes eclipsis, as, an ḃfaca tú? (ăn Wok'-ă thoo) did you see? An ḃfuil tú go maiṫ? (ăn wil thoo gŭ mah), are you well?. See § 257. An ḃfuil sgian agat? Ata. Have you a knife? I have (yes). In the spoken language the an, or at least the n, is usually omitted before consonants; hence 'dtuigeann tú, 'ḃfuil tú are the forms usually heard.
§ 400. Tuigeann sé (thig'-ăN), he understands. Ní ṫuigeann sí (hig'-ăN), she does not understand; an dtuigeann tú? (dhig'-ăN) do you understand?
§ 401. A, her, has no effect on the following consonant; a bróg, her shoe, a ḃróg, his shoe; a mbróg (mrōg), their shoe.
as in English