質問: I saw this sentence on a Japanese teaching site: > > 事故は先週に起こった > > The incident occurred last week > > > I feel very uncomfortable with the に on 先週. This post and this post seem to back up my discomfort. Is this sentence ungrammatical/unnatural or am I missing something?
回答: As a native speaker, I also feel uncomfortable with 事故は先週に起こった, which can be said to be a little unnatural but probably cannot be said to be ungrammatical. 先週 plays the role of an adverb in this sentence, so its natural sentence will be: * 事故は先週起こった。 But as a writer, I would like to avoid this, because I don't like the awkward sequence of Chinese characters of 先週 + 起. So I like this sentence transcribed like this with the use of punctuation marks. * 事故は(、)先週、起こった。 * 先週、事故は起こった。(very natural to me) This point might be trivial for other Japanese, but I am always wondering how to use this kind of noun phrase used as an adverb. In order to avoid this (discomfort), I prefer the following to the above sentence. * 事故は先週のあいだに起こった。(a little longer, but very natural to me) After answering this question, I hit upon the following sentence. * 先週**に**起こった事故は、すごかった。 This sentence with に in it is, no doubt, grammatical and quite natural. I have no idea of the cause of the difference in naturalness and grammaticality between this and the above sentence (事故は先週に起こった).