What is the difference between もう少しで and ほとんど?


Consider these sentences:

  1. (×ほとんど/○ **もう少しで** ) いうのを忘れるところでした。
  2. プールの中の水は、(○ **ほとんど** /○ **もう少しで** ) 満杯である。
  3. 宿題は、(○ **ほとんど** /×もう少しで) 終わった。
  4. (×ほとんど/○ **もう少しで** ) あなたのお家に着きます。

In some cases it is ok to use もう少しで but in others it is not. The same goes for
ほとんど. Sometimes both can be used.

I have heard explanations like ほとんど is mainly used for "possibilities" and are
used for 1-D things like time, distance or level and things that have a
"span". And もう少しで is used for possibilities. But I have no idea what this
means at all.

Can someone explain the grammar behind this and why sometimes they are
interchangeable and sometimes they are not?




English "almost X" can describe two different kinds of situations:

  1. mostly X but not completely X 

>     * It's almost perfect (but is still imperfect).
>     * I almost forgot it (my memory about it is already vague).

  2. X was likely to happen, but it never happened 

>     * I almost died (but I didn't die).
>     * I almost forgot it (but I perfectly recalled it before a problem
> arose).

Now...

  * ほとんど is used _only_ in Situation 1. 

>     * ほとんど完璧です。 It's almost perfect.
>     * 彼はほとんど死んでいるようなものだ。 He's half dead.
>     * 三角関数はほとんど忘れました。 I almost forgot about trigonometric functions.

  * もう少しで is typically used in Situation 2. The pattern to memorize is `もう少しで + ～するところだ`, `もう少しで + ～しそうになる`. You can also use 危うく. See [your own previous question](https://japanese.stackexchange.com/q/56839/5010) and [Learn JLPT N2 Grammar: ところだった (tokoro datta)](http://japanesetest4you.com/flashcard/learn-jlpt-n2-grammar-%E3%81%A8%E3%81%93%E3%82%8D%E3%81%A0%E3%81%A3%E3%81%9F-tokoro-datta/)

>     * もう少しで死ぬところだった。 I almost died.
>     * おっと、もう少しで忘れるところでした。 Oops, I almost forgot.

  * もう少しで can be (usually) used in Situation 1, too. Still, もう少しでX basically means X has not happened yet or X did not happen. Try thinking this phrase as "with a little more time/effort/resource/luck/misfortune/etc, ..." and see if it fits the context. 

>     * もう少しで満杯です。 With a little more water, it will be full.
>     * もう少しで終わります。 With a little more time, it will be done.
>     * もう少しで勝てた。 With a little more luck/effort, we could win. (i.e., we
> lost)
>     * 彼はもう少しで死ぬ。 He will die soon / with a little more damage.
>     * ×もう少しで終わった。 (weird)

Typically, もう少しで is closer to "soon" rather than "almost". Compare:

>   * もう少しで春です。 Spring will come soon (but it has not come yet).
>   * もうほとんど春です。 It's already almost spring (it's warm).
>




English "almost X" can describe two different kinds of situations:

  1. mostly X but not completely X 

>     * It's almost perfect (but is still imperfect).
>     * I almost forgot it (my memory about it is already vague).

  2. X was likely to happen, but it never happened 

>     * I almost died (but I didn't die).
>     * I almost forgot it (but I perfectly recalled it before a problem
> arose).

Now...

  * ほとんど is used _only_ in Situation 1. 

>     * ほとんど完璧です。 It's almost perfect.
>     * 彼はほとんど死んでいるようなものだ。 He's half dead.
>     * 三角関数はほとんど忘れました。 I almost forgot about trigonometric functions.

  * もう少しで is typically used in Situation 2. The pattern to memorize is `もう少しで + ～するところだ`, `もう少しで + ～しそうになる`. You can also use 危うく. See [your own previous question](https://japanese.stackexchange.com/q/56839/5010) and [Learn JLPT N2 Grammar: ところだった (tokoro datta)](http://japanesetest4you.com/flashcard/learn-jlpt-n2-grammar-%E3%81%A8%E3%81%93%E3%82%8D%E3%81%A0%E3%81%A3%E3%81%9F-tokoro-datta/)

>     * もう少しで死ぬところだった。 I almost died.
>     * おっと、もう少しで忘れるところでした。 Oops, I almost forgot.

  * もう少しで can be (usually) used in Situation 1, too. Still, もう少しでX basically means X has not happened yet or X did not happen. Try thinking this phrase as "with a little more time/effort/resource/luck/misfortune/etc, ..." and see if it fits the context. 

>     * もう少しで満杯です。 With a little more water, it will be full.
>     * もう少しで終わります。 With a little more time, it will be done.
>     * もう少しで勝てた。 With a little more luck/effort, we could win. (i.e., we
> lost)
>     * 彼はもう少しで死ぬ。 He will die soon / with a little more damage.
>     * ×もう少しで終わった。 (weird)

Typically, もう少しで is closer to "soon" rather than "almost". Compare:

>   * もう少しで春です。 Spring will come soon (but it has not come yet).
>   * もうほとんど春です。 It's already almost spring (it's warm).
>

