や否(いな)やAs soon as, No sooner than, The minute

や否(いな)や, like か否(いな)か, is a grammar pattern that makes use of 否(いな) 'no', an interjection. However, unlike the pairing with the adverbial particle か 'or' when stating 'whether or not (A)', the pairing of 否(いな) with や in its role as a conjunction particle has the meaning of 'as soon as (A)', or 'no sooner than (A)'. Remembering that や simply highlights the word before it is not being limited to that, the literal meaning of や否(いな)や is 'at a point when neither (A) or not (A) could be determined, (B)'.

や否(いな)や will be used after verbs in their dictionary form.

• 私(わたし)が部屋(へや)から出(で)てくるのを見(み)るや否(いな)や、空(あ)き巣(す)が手(て)に持(も)っていたものを私(わたし)に投(な)げて、逃(に)げていった。

  As soon as the burglar saw me coming out of the room, he threw everything that was in his hand at me and ran away.
• 俺(おれ)の顔(かお)を見(み)るや否(いな)や友達(ともだち)の犬(いぬ)が吠(ほ)え出(だ)した。

  As soon as he saw my face, my friend's dog started barking.
• 彼(かれ)は席(せき)に座(すわ)るや否(いな)や「とりあえず生(なま)一(ひと)つ」といった。

  He said 'I'll have a beer to start' as soon as he sat down.

や否(いな)や is a formal expression that will generally be used when (B) is something that happens spontaneously, or is surprising.

Caution

As や itself carries the 'not limited to' meaning, it is also possible to see this structure with the 否(いな)や part omitted. In these situations, the meaning will not change at all. や in this case behaves similarly to か when presenting a question in the middle of a sentence, and sounds like 'when not certain that (A), (B)'.

• 彼(かれ)は本(ほん)を開(ひら)くや、寝(ね)た。

  He fell asleep as soon as he opened the book.
• 彼女(かのじょ)はあの曲(きょく)を聴(き)くや、泣(な)き始(はじ)めた。

  She started to cry as soon as she listened to the song.