The differences between ～がたい、〜にくい、〜づらい


I was wondering what the differences are between these three: ～がたい、〜にくい、〜づらい

They all seem to be some sort of variant of "Hard to do ~". But it seems they
are used with different verbs and/or imply slightly different things. However,
I'm not sure on what these are.

Questions:

1) When should you use one of these over the others. For example, when should
you use ~がたい over ～にくい and ～づらい

2) What is the difference (and are all 3 acceptable?) between:

  1. わかりがたい 
  2. わかりにくい
  3. わかりづらい




Great question! Here's how I understand them:

### ～にくい 【～難い】

The most general of the three. Basic "hard/difficult to do ～" meaning.

### ～づらい 【～辛い】

You can see that it comes from `辛【つら】い` which can mean "difficult" or
"painful". So `～づらい` is usually a more subjective meaning, whereas `～にくい` is
usually more objective. Also, `～づらい` is limited to actions that are
intentional.

### ～がたい 【～難い】

Very difficult to do. "Virtually impossible". The most expressive of the
difficulty.

So I would say that `(～にくい <=> ～づらい) <<< ～がたい`. Also notice that `～にくい` and
`～がたい` have the same kanji. In practice, I don't think they're ever written in
kanji, but if you were to see it, I don't know if even the sentence context
would help you know which one it was.

>   2. What is the difference (and are all 3 acceptable?) between:
>

>   1. わかりがたい
>   2. わかりにくい
>   3. わかりづらい
>

Yes, they would all be acceptable, but would be used in different
scenarios/contexts according to the definitions (exercise left to the reader).

**UPDATE** ー According to the PDF posted by @Derek Schaab below, `分かりがたい` is
not acceptable because `分かる` is not an 意志動詞. However, `理解しがたい` is acceptable
in its place.

**NEXT UPDATE** ー I wanted to add this example that I've been thinking of for
a while. Hopefully it will be helpful to someone.

>   * [バンド名]の好きな曲は何？ → What is your favourite song by [band name]?
>   * 選びにくい………てか、選びづらいのだ。まー、やっぱりそれよりも選びがたい。 → (roughly) It's hard for me to
> choose....rather, it kind of hurts my brain to try to choose one. Actually,
> it's almost impossible for me to pick (which one).
>

