English translation:
hard to
difficult to
Structure:
Verb[stem] + がたい
Explanation:
[nearly impossible to…]
Okay I still don’t know what the exact difference between にくい、づらい、and がたい is and I’ve read conflicting descriptions of them all.
First from the Resources linked by BP:
Tae Kim Link
「にくい」 tends to be used for physical actions while
「がたい」 is usually reserved for less physical actions that don’t actually require movement
「づらい」more coarse variation of stem + 「にくい」
JStackExchange Link
～にくい 【～難い】
The most general of the three. Basic “hard/difficult to do ～” meaning.
～づらい 【～辛い】
～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. Only used with 意志動詞
And other resources I’m using.
日本語の森 Link
がたい is formal version of にくい & づらい
にくい is for physical actions. (物理的）
づらい is for psychological actions. （心理的）
完全マスターN2文法
能力的にできないという意味では使わない。主に心の働きを表す動詞（想像する・理解する・信じる等）や発言を表す動詞（言う・表す等）につく。
My translation: Not used to mean unable to do something due to lack of ability. Mainly attached with verbs that express mental functions (to imagine, to understand, to believe, etc.) or speech verbs (to say, to express, etc.)
So from all this, my understanding is にくい is used for physical, objective actions. づらい is used for more psychological, subjective, intentional actions. がたい is used for… intentional actions that aren’t usually physical?
I’m asking mainly because there’s a question in Kanzen Master book that has all three:
みんなの信頼を裏切るなんて、（ ）ことだ。
a 許しがたい
b 許しにくい
c 許しづらい
And even though I answered it correctly and I know it’s A, I can’t explain from the above descriptions why C can’t be the right answer as well.
4 Likes
Hey 
To sum up:
First of all にくい is the broadest term. It doesn’t have restrictions like the other two. Also, it describes objectively that something is hard. It can be used with transitive and intransitive verbs.
づらい describes speaker’s/writer’s aversion/reluctance to do something That is why it is more subjective. Also, it cannot be used with intransitive verbs.
電気が消えにくい。 〇 The light is hard to turn off.
電気は消えづらい。 X
がたい is more formal than the rest. It is also like Stack answer said used to describe that something is impossible or almost impossible. So it is much stronger than “hard to”.
Therefore answer A, since 許しがたい means that it is absolutely intolerable. Unforgivable.
Not to mention 許しがたい is basically a fixed expression. I haven’t seen 許しづらい。
3 Likes
Thank you so much for your reply! That clears it up a lot!
I realize they’re all saying the same thing but Tae Kim and 日本語の森 are just over-simplifying it. 完全マスターN2文法 doesn’t talk about the the impossibility emphasis.
Textbook case of why multiple sources are important.
1 Like
That is because of space, kanzen master is a book made for reviewing rather than learning. 
These videos might be worth adding:
2 Likes
I usually only do my drills with the english translations, which makes this sentence in particular pretty frustrating
can bunpro add the 辛い as a separate grammar point. In my practical case, i didnt use and know about it at all and accidentally come on it on a (all n4 grammar youtube video) to polish my grammar skill. If you know the nuance, its pretty useful.