際に|さいに
Means "when," "at the time of," or "on the occasion of" something. It is a formal counterpart of とき, often used for procedures, rules, or notable occasions.
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Used in formal speech and writing such as official notices, instructions, business communication, and announcements. It describes when a procedure applies or what happened on a particular occasion. It sounds noticeably stiffer than とき, which is preferred in casual conversation.
Do not use 際に for trivial everyday moments in casual talk; とき sounds much more natural there.
Note that a noun must be followed by の before 際に, as in 入国の際に.
Note that a な-adjective keeps な before 際に, as in 必要な際に.
- に際してN2「に際して」is more solemn, used mainly for major matters such as meetings and contract signing and for formal procedural explanations. It attaches directly to nouns without 「の」 and only to verbs in dictionary form; in formal contexts the two are mostly interchangeable, but 「際に」 is preferred in ordinary situations.
- にあたってN2「にあたって」is typically preceded by major matters such as holding a meeting or studying abroad, and emphasizes giving a speech, making a statement, or preparing in the face of that occasion. It attaches only to verbs in dictionary form and directly to nouns without 「の」; it sounds more formal, while 「際に」 is common for ordinary procedural explanations.
- にあたりN2「にあたり」is mostly used on the occasion of setting out to do something as planned, and what follows is often a speech, a statement, or preparations, giving a more formal tone. It attaches directly to nouns without 「の」 and only to verbs in dictionary form; it is generally not used for unexpected accidents.
- 〜に先立ってN2「に先立って」refers to doing preparations etc. 'before' a formal or major event, whereas 「際に」 refers to the moment or occasion when the event takes place—the time points differ, so they are generally not interchangeable. 「に先立って」attaches to nouns without 「の」 and is more written-style.
- において / におけるN3「において」is the written-style equivalent of 「で」, indicating the place, time, occasion, or field in which something occurs; it attaches directly to nouns, with 「における」 used to modify nouns. 「際に」focuses on the timing of doing something and can also attach to verbs, so the two are generally not interchangeable.
に際して and にあたって/にあたり are even more formal and stress facing a special undertaking or occasion, often with a sense of preparation or resolve. 〜に先立って means "prior to" something, and において/における marks the place, field, or situation rather than the moment of an action.
