Since my recent question about 〜く＋ある, I've been trying to learn more about the differences between 形容詞「無い」 and 助動詞「〜ない」. In other words, I'm trying to learn how the independent adjective nai and the negative verb suffix -(a)nai are different.
We have a question about whether verbs ending in 〜ない are adjectives already, and in one answer, a user writes that the negative verb 食べない can't take the suffix
-さ, so *食べなさ is unacceptable. I was curious whether that was true of all verbs, so I decided to search for
なさ in the Balanced Corpus of Contemporary Written Japanese (BCCWJ). Unfortunately, this had a lot of false positives due to forms like
〜なさすぎる, and verbs like
なさる, and so on.
To filter out false positives, I decided that I needed to search for a more specific example. The form I chose was
分からなさ, because regardless of whether it's correct or not, it made sense to me. I was able to find only one example in BCCWJ, and it was taken from the web portion of the corpus:
This example seems very informal, and I suppose the author wasn't worrying about writing "properly". I was able to find more examples on Google by searching for 意味の分からなさ, some of which seemed a little bit less informal:
I'm not sure if I can draw any conclusions from these examples. My guess is that using
-さ like this is only acceptable informally, judging by how I can find results online but not in published books. But I suppose it's also possible that the results I've found are very unusual, or that I've misunderstood what
-さ is doing in these examples.