I am struggling with those two possible meanings, and have found two examples that typically puzzle me:

  1. 「この問題できる?」「こんなのわけないよ」

  2. 「N2の試験に合格したんだって?」「そんなわけないだろう」

(taken from Nihongo So-Matome N2 book)

First one is given as holding the "easy" meaning, second one, the "no way/impossible" meaning... although for me their writing here seem almost identical.

I can see that the first one has this の inside, and that probably impacts the meaning! But can someone develop around it, and tell me what is going on here that makes the meaning differ ?

I've found somewhere that the "easy" meaning can be deciphered when the expression is used as an adjective, which concurs with Jisho too. But here, it is not as far as I can understand.

Maybe also on a more fundamental level, how such an expression (わけ(が・は)ない)can have two such opposite meaning ?

2 Answers 2


What you see is a result of two subtle (but basic) grammar points combined.

  1. こんなの/そんなの vs こんな/そんな

    こんな/そんな… are (technically not adjectives, but) a kind of single function adjectives, that are only allowed to qualify a noun.

    の has tons of meanings, among which is nominalization. When の comes after 連体形 (form used to qualify a noun) of adjectives or verbs, it can make a noun phrase e.g. きれいなの "beautiful one", 走るの "something that runs". Thus こんなの/そんなの… are nouns as a whole.

  2. わけ (noun) vs わけ (形式名詞 "formal noun")

    わけ has multiple meanings as a noun, but aside from that, it is most often used as a 形式名詞, which grammatically behaves as if a noun, but always needs a qualifier and serves as a function word in meaning.

Now, わけ + ない creates two idiomatic expressions:

  • わけ (noun) (+ optional particles) + ない
    "no reasoning needed" = "is no-brainer"
  • X わけ (形式名詞) (+ optional particles) + ない
    "there is no way X", "it cannot be X"


The first sentence starts from こんなの, which is a noun, impossible to qualify the next わけ. So this sentence can be only parsed as "こんなの [omitted topic particle] わけない".

The second sentence starts from そんな, and it must qualify the next わけ, thus this わけ is a 形式名詞. The sentence is parsed as "そんなわけ [omitted particle] ないだろう".


The real meaning of wakenai is "no understanding" or "no reason", so I'd translate your sentences as:

Can you do this question? You asking me makes no sense, of course.

With the "yo" translating as "of course".

The second sentence:

Did you pass the N2 exam? That thing makes no sense to me.

So the meaning of "wakenai" differs based on context.

  • 3
    You asking me makes no sense... -- でもこの辞書の例文のように dictionary.goo.ne.jp/word/%E8%A8%B3%E7%84%A1%E3%81%84 「問題をわけなく解いてみせる」の「わけない」だったら? または、誰にも聞かれてないけど、自分から「こんな問題、わけないさ!」とか「こんな仕事、わけないさ!」って言ったら?
    – chocolate
    Sep 5, 2022 at 7:43

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