際に, に際して, にあたって

Question

I'm very confused about these grammatical forms: all of them are translated as "at the time, on the occasion of", and I can't understand the differences. I found some answers and grammatical points on these forms (this and this), and I tried to hit my grammars about them; as far as I understood, the latter two forms are formal and one can usually replace the other.

Moreover, in this answer the answerer said that «「A に際して B」 is more like "B taking A as an oppotunity"», but this sounds odd with this example from the grammar site linked above: 「車を買うに際しては、保険に入らなければならない。」; I understand the sentence, but "You must buy an insurance taking buying a car as opportunity" sounds very odd to me, since you don't buy the insurance taking the car as opportunity, you buy the insurance because you must have one if you have a car.

In all of this it doesn't seem that 「際に」 is just a less formal version of the other two, but I don't relly understand how these three forms differ.

Answer 1

They all have similar meaning - namely, "faced with X". IMO 際に and 際して has the same nuance, except that 際して is more formal. All three expressions are neutral and don't imply what needs or can be done is positive or negative.

There are differences between 際に, 際して vs. にあたって.
- にあたって can be used for events that occur earlier than 際に, 際して
- にあたって implies the action is done in anticipation

For example:

(1) 帰国に際し写真を撮った
(2) 帰国にあたって写真撮った

Suppose the photo was taken 6 months before flying back. (2) would be perfectly fine, whereas (1) would be a stretch.

Another example:

(1) 帰国に際し死亡した
(2) 帰国にあたって死亡した

(1) is ok, while (2) is very odd because one wouldn't die in preparation of returning to the home country.