1. The accident happened on a stormy night.
2. The accident happened at a stormy night.
#1 is correct, but I don't understand, why must we use "on" instead of "at" here, whereas we usually say "at night". e.g.: He came home late at night. Thanks a lot.
Hi, I would think the first one is perfectly right,
when we say at night, that is ligitimate, because it is a set phrase,
then a grammatical rule goes like this: when there is any modifiying word goes before night, the preposition should be nothing but "on". That is the rule as was set in grammar...e.g.on a moon-lit night, in the night---on a chilly winter night in November of lunar calendar
I think celine713 is absolutely right. 'On' in this case is the usual abbreviation of 'on the occasion of' and thus refers to a specific night, ie a stormy one. 'At night' only means 'at the night time of day'. Thus, celine713's rule of any qualifying adjective is totally right. I wish we had people like her teaching in our English schools....