Hello,
I thought, while using verbal nouns, we didn’t need to use “を”. But I saw some examples and I am confused.
凶器に残された指紋は容疑者のものと一致する
“一致” is a verbal noun and here, there is no “を”. (icchisuru)
数学の授業中に私は居眠りをした
“居眠り” is also a verbal noun but there is “を” here. (inemuri wo shita)
Why? Thank you.
Both are correct, and in simple examples, the meaning is the same.
Just be careful, 居眠りする acts as a single verb, while 居眠りをする is a noun + verb combination, so the grammar around the expression will change.
E.g. 数学を勉強をする is ungrammatical, it’s either 数学を勉強する or 数学の勉強をする.
Depending on the word, one of them might be more common/natural than the other though, or the emphasis might differ, and some grammar can only be used with one over the other. See these two examples:
Thank you for the answer.
As far as I can understand, mostly you choose it based on how common/natural they are. It seems it is something I shouldn’t focus as a beginner, in the end for most cases, I will be understood and be correct gramatically. Also of course, I should be careful about grammar usage.
Essentially yes, a good rule of thumb for “naturalness” is that two kanji compounds with no okurigana(the kana after the word eg 飲む ->む) tend to drop the を like 勉強する while those with okirigana tend to have the を like 居眠りをする.
Not a rule but a tendency. The reason has to do with the origin of the words coming from old Chinese or old Japanese.