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The words 一瞬{いっしゅん}, 瞬間{しゅんかん} and 一瞬間{いっしゅんかん} all seem to mean "instant",
"moment". Is there any difference between them?
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2017-04-16T15:17:39.007
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2017-05-09T05:15:44.903
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word-choice words nuances
Are there differences between 一瞬{いっしゅん}, 瞬間{しゅんかん} and 一瞬間{いっしゅんかん}?
一瞬{いっしゅん} and 瞬間{しゅんかん} are natural Japanese words, but we don't usually use
一瞬間{いっしゅんかん}.

## As nouns

一瞬 and 瞬間 are nouns.

瞬間 can be used to make a compound word, such as
[瞬間{しゅんかん}湯沸{ゆわか}し器{き}](http://jisho.org/word/%E7%9E%AC%E9%96%93%E6%B9%AF%E6%B2%B8%E3%81%97%E5%99%A8)
(which means _instant water heater_ , i.e., _tankless water heater_ ), while
一瞬 can not.

## As adverbs

一瞬 can also be an adverb, which is used like:

  * 一瞬{いっしゅん}、彼{かれ}は立{た}ち止{どま}った。
  * 彼{かれ}は一瞬{いっしゅん}立{た}ち止{どま}った。
  * (He stopped walking and stood still for a short time.)

But you _can't_ say:

  * 瞬間{しゅんかん}、彼{かれ}は立{た}ち止{どま}った。
  * 彼{かれ}は瞬間{しゅんかん}立{た}ち止{どま}った。

Instead, 瞬間 can be an adverb with 「に」, which is used like:

  * 瞬間{しゅんかん}にお湯{ゆ}が沸{わ}く。
  * 瞬間{しゅんかん}にお湯{ゆ}が沸騰{ふっとう}する。
  * (The water boils after a very short time.)

The following illustration depicts the difference between 瞬間に and 一瞬:

[![difference between 瞬間｛しゅんかん｝に and
一瞬｛いっしゅん｝](https://i.stack.imgur.com/jHEyl.jpg)](https://i.stack.imgur.com/jHEyl.jpg)

Therefore, you can also say 「一瞬｛いっしゅん｝お湯｛ゆ｝が沸｛わ｝く」, but it has a different
meaning: the water boils for a brief specific duration, not before, not after.
That is, the act of boiling lasts a short time.

* * *

**Edit to address comments:**

Why 「瞬間に、彼は立ち止まった」 or 「彼は、瞬間に立ち止った」 could not be said? Consider the following
sentences, all using the adverb 「瞬間に」 which means "in a short time":

  1. 彼｛かれ｝は瞬間｛しゅんかん｝に立{た}ち止{どま}った。
  2. 彼{かれ}は瞬間{しゅんかん}に立{た}ち上{あ}がった。
  3. 鳥{とり}たちは瞬間{しゅんかん}に飛{と}び去{さ}った。
  4. 猫{ねこ}はびっくりして瞬間{しゅんかん}に飛{と}び上{あ}がった。
  5. 鳥{とり}たちは物音{ものおと}にびっくりして瞬間{しゅんかん}に飛{と}び去{さ}った。

They seem grammatically correct, but only the first one does not sound natural
as Japanese. Why does this happen? I could not get the exact answer at hand,
but I conjectured the answer as follows:

Generally, it is difficult for a moving object to stop suddenly without any
residual movement because of an inertial force. If I am allowed to use the
term in the illustration, I could say that if the state A describes something
moving and the state B describes the state of standstill of the same thing,
the transition to the state B in a very short time is difficult, therefore the
sentence does not sound natural.

On the other hand, the other four sentences express a sudden shift to a state
with movement, and I think that therefore they sound natural. You can easily
judge whether a certain thing is moving or not, so the state of standstill is
more strictly judged than the state of movement.

I found it interesting that the logical understanding of physics affects a
Japanese sentence.

**Evidence for logical Japanese sentences**

As I said the sentence 1 does not sound natural, because it is not
scientifically logical. But you could make the sentence 1 natural by adding an
appropriate phrase to it like "no way", "he told a lie", "it's impossible" "to
my astonishment", "with some fluctuations" "almost/nearly", etc. which make
the meaning of the whole sentence logical. Then, the following sentences
including the sentence 1 sound natural as Japanese.

  6. 彼｛かれ｝は瞬間｛しゅんかん｝に立｛た｝ち止｛ど｝まった **と言｛い｝ったがそんなの嘘｛うそ｝だよね** 。
  7. **びっくりしたなぁ、** 彼｛かれ｝は瞬間｛しゅんかん｝に立｛た｝ち止｛ど｝まった **よ** 。
  8. **少｛すこ｝しよろけたが** 彼｛かれ｝は **ほぼ** 瞬間｛しゅんかん｝に立｛た｝ち止｛ど｝まった **よ** 。
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