Meaning and usage of よほどのこと


In [this answer](https://japanese.stackexchange.com/a/76458/7944) it is
incidentally mentioned that よほどのこと means "something very
unusual/extraordinary". I'm struggling to find this definition in a
dictionary, no matter whether I look up the whole phrase or just よほど on its
own. Though I did find it in a thesaurus with a synonym of 珍しい quite some way
down the list.

It seems to come up most often in a Google search as よほどのことがない限り. Would it be
safe to say that this can be treated as a set phrase? I see in the answer I
linked that it is used as よほどのことがあった so I guess that's not quite the right
answer.

In summary

  1. How does よほどのこと come to mean "something very unusual"?
  2. In which contexts/grammatical constructs is it safe to use?
  3. Is it a common phrase?




よほどの/よほどな is a very common adjective that means "unusual/extraordinary
**(enough to explain/justify something)** ". The part in parentheses is
important; this adjective is used in relation to another exceptional/unlikely
event that needs explanation or justification. よっぽどの/よっぽどな is a synonym
(sounds more colloquial). よほど/よっぽど also works as a standalone adverb.

余程 mainly modifies words related to "situation", such as こと, 事情, 状況, わけ, and
理由. But 余程のこと by itself is not a set phrase, and 余程 can modify almost any
noun, as shown below.

Good Examples:

  * 余程の{理由/こと/事情}がない限り出席してください。  
Please attend unless you have a very good reason not to do so.

  * 余程の力で叩かないとこの扉は壊れないはずだ。  
This door should not break unless you hit it with a extreme force.

  * 娘を喜ばせるには、よっぽどのプレゼントじゃないとダメだろう。  
I'll need a really good/special present to please my daughter.

  * 彼が泣いた? よっぽどだったんだな。  
He cried? Then it must have been very intense.

  * よっぽどお金がないんだろう、彼は毎日パンだけ食べている。  
I guess he has very little money; he is eating only bread every day.

WRONG examples:

  * × 彼は余程の人です。(This does not mean "He is unusual.")
  * × 彼はよっぽど強い。(This does not mean "He is very strong." Use とても/すごく/etc instead.)

Actually these might have been acceptable many years ago, but you should not
say them in modern Japanese.




よほどの/よほどな is a very common adjective that means "unusual/extraordinary
**(enough to explain/justify something)** ". The part in parentheses is
important; this adjective is used in relation to another exceptional/unlikely
event that needs explanation or justification. よっぽどの/よっぽどな is a synonym
(sounds more colloquial). よほど/よっぽど also works as a standalone adverb.

余程 mainly modifies words related to "situation", such as こと, 事情, 状況, わけ, and
理由. But 余程のこと by itself is not a set phrase, and 余程 can modify almost any
noun, as shown below.

Good Examples:

  * 余程の{理由/こと/事情}がない限り出席してください。  
Please attend unless you have a very good reason not to do so.

  * 余程の力で叩かないとこの扉は壊れないはずだ。  
This door should not break unless you hit it with a extreme force.

  * 娘を喜ばせるには、よっぽどのプレゼントじゃないとダメだろう。  
I'll need a really good/special present to please my daughter.

  * 彼が泣いた? よっぽどだったんだな。  
He cried? Then it must have been very intense.

  * よっぽどお金がないんだろう、彼は毎日パンだけ食べている。  
I guess he has very little money; he is eating only bread every day.

WRONG examples:

  * × 彼は余程の人です。(This does not mean "He is unusual.")
  * × 彼はよっぽど強い。(This does not mean "He is very strong." Use とても/すごく/etc instead.)

Actually these might have been acceptable many years ago, but you should not
say them in modern Japanese.

