means "on the occasion of" an important event: a graduation, a
wedding, an opening, a departure. It goes after a noun or a verb in the
dictionary form, and the rest of the sentence says what is done at that
moment.
、。
On the occasion of my graduation, I want to thank my teacher.
、。
When entering into a contract, please confirm the conditions.
、。
On the occasion of your marriage, I offer my heartfelt congratulations.
It is formal: speeches, announcements, letters, official notices. means the same and is a little stiffer still, and modifies a
noun.
、。
On the occasion of the opening, I would like to say a few words.
。
Please read the precautions for departure.
に際して or 時
works for any "when". に際して is only for an occasion that happens
once and matters, so an everyday routine takes 時.
、。
I turn off the water when I brush my teeth.
is close in meaning and formality. It leans towards preparing
for what is coming; に際して is about the moment itself.
Lingaku