This question is based on the discussion arising from "Unsolvable Problem"
Start of Excerpt
Relevant discourse extracted from "Unsolvable Problem":
Quoted from Derek Schaab's reply to "Unsolvable Problem":
○ (私は)この問題{もんだい}が解{と}けない。 [I] can't solve this problem.
× この問題は解けられない。 This problem can't solve itself.
The second sentence might sound fine at first (from a grammatical standpoint), but when you think about it, assigning an ability to an inanimate subject doesn't work here. (Even in English, the better way to express the idea behind sentence #2 is, "This problem will not solve itself.")
Because of this, only 解{と}けない問題 is correct.
Also from Derek Schaab's reply to "Unsolvable Problem":
istrasci also mentioned the
~にくい
suffix. I was about to agree with this, but then I saw sawa's edit which reminded me that解く
can be read as bothと
く
andほど
く
, and解ける
can be read as bothと
ける
andほど
ける
. (The meanings differ between readings.)~にくい
can be attached to bothほどく
andほどける
, such as in this way:ほどきにくいくつひも a shoelace that is difficult to untie
ほどけにくいくつひも a shoelace that won't come undone easily
…and to
とく
, but not toとける
:○ ときにくい問題 a problem that's difficult to solve
× とけにくい問題
End of Excerpt
(Question 1) Why is ほどけにくい
acceptable while とけにくい
unacceptable? Following the logic of "I cannot assign ability to an inanimate subject", it should cause both to be unacceptable since both are intransitive and by extension force the existence of the "inanimate subject"
(Question 2) If it is true that there are cases for which Intransitive+にくい
are acceptable, does it imply that there are cases for which Intransitive+られる
(Potential form) are acceptable?
(EXTRA Question 2.1) If there are cases for which Intransitive+られる
(Potential form) are acceptable, how do we decide if we can assign ability/potential to an inanimate subject?
Appendix: Other points taken from the comments in "Unsolvable Problem" for your consideration
From Derek Schaab:
Could it be related to whether the verb expresses a continuous or discrete change?
~にくい
, when it meansなかなか~しない
, seems to imply that the verb may happen only gradually over a period of time, but never quickly and easily. Because of the gradual transition, a continuous-change verb (such asほどける
or燃{も}える
) is required. But解{と}ける
expresses a discrete change: a problem is either solved or it isn't, and the change from unsolved to solved takes place instantly. Perhaps this is why解{と}けにくい
sounds odd, but other combinations, such as溶{と}けにくい
, work.From Matt:
But you can say
割{わ}れにくい
, and that is instantaneous. Perhaps〜eにくい
has some sort of restriction relating to concrete vs abstract subjects?