I know the following two sentences give implication that "not expecting me to understand (it)" but I have a feeling that they give different nuances that I just can't put my finger on:

それは分{わ}かるわけがないでしょう。 sore wa wakaru wake ga nai deshou.

それは分{わ}かるはずがないでしょう。 sore wa wakaru hazu ga nai deshou.

Would someone explain what is the difference of the two sentences, and also how to choose between using はず and わけ?


6 Answers 6


disclaimer: not a native speaker

I think 'wake' implies that things happened as expected, where as 'hazu' implies that what happened is not what was expected.

Or, 'wake' is a bit more neutral, a "matter of fact", where as 'hazu' is more of a personal opinion/subjective kind of thing.

This is how I would understand the difference:

それは分かるわけがないでしょう。 sore ha wakaru wake ga nai deshou.

You're not meant to understand this .. it's normal.

それは分かるはずがないでしょう。 sore ha wakaru hazu ga nai deshou.

I see no reason you could understand this .. so what's going on?

  • 2
    Hasen J is right here in that "hazu" means that the speaker is surprised by the outcome of something. I'd say that "wake" is more assertive in the example given, effectively stating that there's no way the other person could possibly understand so-and-so.
    – rcjsuen
    Commented Jun 1, 2011 at 1:49
  • 1
    Yes, 'wake' has the connotation that "objectively" it is the way it is. Hasen J wrote "it's normal" which is a good way to help incorporate it into everyday speech.
    – crunchyt
    Commented Jun 7, 2011 at 6:09

I'd translate them as follows:

分かるわけがないでしょう。 Wakaru wake ga nai deshō.

"There's no way (he) can understand this." or "(He) surely doesn't understand this."

分かるはずがないでしょう。 Wakaru hazu ga nai deshō.

"I don't think (he) understands this."

はず is more of a personal inkling, while わけ is more of an objective/direct/strong statement. Depending on how it's meant わけ can be used insultingly:

出来るわけないだろう。 Dekiru wake nai darō.

"(You) can't (are unable to) do that!" or "Are (you) crazy to think (you) can do that?"

出来るはずはないけど… Dekiru hazu wa nai kedo…

"(I) don't think (you) can do it, but... (maybe I'm wrong about that)"

More, negated examples:

出来ないわけがないでしょう。 Dekinai wake ga nai deshō.

"It's not impossible, right?" or "It should be possible, right?"

出来ないはずはないですが、今は難しいです。 Dekinai hazu wa nai desu ga, ima wa muzukashii desu.

"I don't think it's impossible, but it's very difficult right now."

  • 分かるはずがないでしょう。 Wakaru hazu ga nai deshō. I think a better translation is "I think it's impossible he understand this" or "He shouldn't understand this"
    – Uberto
    Commented Jun 1, 2011 at 10:10
  • 4
    ないだが is ungrammatical.
    – dainichi
    Commented Feb 8, 2012 at 13:02

Wake is a reason or cause; hazu is an expectation. They can be used in the same context, but still have a different sense.

分かるわけない! "How would you understand?!" (there's no reason to think you would get this) わかるはずはない "He shouldn't understand" (I expect that he doesn't).


I believe the difference emphasis.

それは分かるわけがないでしょう。 sore ha wakaru wake ga nai deshou. - I'd read this as わかりようがない

それは分かるはずがないでしょう。 sore ha wakaru hazu ga nai deshou. - and this as he doesn't have a chance to understand this. This is the stronger of the two.

  • what does わかりようがない mean?
    – Lukman
    Commented Jun 1, 2011 at 1:36
  • He doesn't have the ability to understand. All three are very similarly related. Might want to add it as an expansion on your question. Commented Jun 1, 2011 at 1:38
  • 1
    Not sure I'd agree with はず being the stronger of the two. It really depends on the context and how it's spoken.
    – deceze
    Commented Jun 1, 2011 at 1:48
  • Wow, I haven't seen 〜ようがない since JLPT grammar books. It's a good one, deserves more use than it gets :)
    – makdad
    Commented Jun 1, 2011 at 3:09

I would expect the わけ version to be stronger. If you look at the meaning of わけ and はず in isolation, わけ means 'reason' - eg, in the pattern of 「どうしてそうなったの?/〜〜〜〜したわけ。」 はず however expresses an expectation - 「こうなるはず。」 Thus, if you use わけ, you imply that you can't understand why such a situation would happen; with はず, you imply that you simply wouldn't expect such a situation to happen (or, retrospectively, you express that you, previously, strongly expected it not to happen)

  • would you say that Wake is opinionated as Hazu is? Commented Jun 1, 2011 at 1:36
  • Ignore my previous comment; I had misread the question. I would consider either one to be opinionated in this particular case (as it's hard to be objective about the psyche of other people), but はず is probably more opinionated
    – bdonlan
    Commented Jun 1, 2011 at 1:41

Disclaimer: Not a native speaker.

Based on how I hear it being used and also from the goo dictionary usage explanation, I don't think the difference is that much (as to be worried about when to use which).

Even if the dictionary gives different example sentences for the usage:




They club it together in the "proper use" section

[使い分け] 【1】「わけがない」「はずがない」は、…する理由がない、…する道理がない、の意味で、ある事態の起こる可能性が全くないことを表わす。「わけはない」「はずもない」などの形もある。

To me, its as simple as:

わかるはずがない: (I wasn't in town,so)How would I know?(what happened to him)

わかるわけがない: (I wan't in town,so)No way of knowing(what happened to him)

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