た拍子に|たひょうしに

1. 1At the moment of an action, and triggered by it, something unexpected or accidental happens.Ex. 1
2. 2In 何かの拍子に, something happens by chance, triggered by an unspecified cause.

Used in both speech and writing to describe accidental, unplanned results sparked by an action or movement. The result is often something the speaker could not control, so it frequently combines with てしまう. Compared with たとたん, which simply marks "right after", た拍子に stresses that the first action physically or causally set off the second.

• たとたんN3「たとたん」 only emphasizes that the two events occur almost simultaneously; the first clause need not be the cause of the second, and even predictable results can be used. 「た拍子に」 stresses that the impact of the first action directly triggers something unexpected. When the first action does trigger an unexpected result, 「たとたん」 can be substituted.
• が早いかN1「が早いか」 only emphasizes that the two actions occur with an extremely short, almost simultaneous interval; it does not require the first action to cause the second, and the second is not limited to unexpected results. It attaches to the dictionary form or た形 and is mostly used in written narration. The two patterns generally cannot be interchanged.
• や否やN1「や否や」 only emphasizes that two events happen one right after the other, with no causal requirement, and the second event can be an intentional action by the subject. It attaches to the dictionary form of verbs and has a strong written flavor. 「た拍子に」 focuses on the momentum of the first action triggering something unexpected, attaches to た形, and is neutral in register.
• なりN1「なり」 attaches to the dictionary form and is rather literary, indicating that the second event occurs immediately after the first, often as a surprising action. 「た拍子に」 attaches to た形 and emphasizes the impact of the first action causing an unintended, unexpected result; the two are generally not interchangeable.
• かと思ったら / かと思うとN2「かと思ったら / かと思うと」 focuses on the contrast between the two clauses and how quickly things change; no causal link is required, it mostly describes other people or things, and it also carries the meaning 'I thought... but...'. 「た拍子に」 emphasizes an action's impact directly causing the unexpected and can be used about oneself. The two generally cannot be interchanged.
• ところをN2「ところを」 indicates being seen, caught, or stopped while in the middle of some situation, or is used in polite set phrases like 「お忙しいところを」. 「た拍子に」 describes the momentum of an instantaneous action coincidentally causing an unexpected result; the two cannot be interchanged.

Unlike たとたん, が早いか, や否や and なり, which mainly express immediate succession (が早いか, や否や and なり often introduce a quick, sometimes deliberate follow-up action), た拍子に says the first action caused an accidental result. かと思ったら marks the speaker's surprise at a sudden change, and ところを refers to a situation someone is in the middle of (e.g. being seen or interrupted); neither expresses an action triggering an accident.