I know とても is not very formal, but what about ずいぶん and 大いに? Are ずいぶん and 大いに interchangeable, and if so, which is more formal?

  • 1
    I can't explain why but 大いに sounds far less colloquial than ずいぶん to me... and one difference I can think of: 〇「大いに頑張ってくれ!」×「ずいぶん頑張ってくれ!」
    – chocolate
    Commented Feb 14, 2017 at 1:07

2 Answers 2


What is formal in your mind?

Suppose the meeting room is a mess and you want to have it clean. The following is the e-mail message from you to a person in the General Affairs Department.

"会議室がとても汚れています。11時までに、清掃をお願いします。" This is the best and most popular (and formal) expression on business.

"会議室がずいぶん汚れています。・・・" This one is also OK.

"会議室が大{おお}いに汚れています。・・・" This one is acceptable but "おおいに" is generally for the expression of an emotion. I wouldn't use it for this situation.

"会議室が非常{ひじょう}に汚れています。・・・" The word "非常に" is versatile. It's used widely. I can recommend the use of "非常に" for any situation without using set phrases.

"非常に" と言う言い方は、非常に広く使われます。

The common expressions,

Preceding sentence: "とてもご無沙汰しております" Long time no see. (I'm not sure but "とても" in English here can be "very"? Very long time no see.???)

"おおいに" is rather suitable for the expression of feeling.

"私は、その素晴らしい演奏に、大いに感動した" I was greatly moved by the performance.

  • 「とてもご無沙汰しております」って、言うんですか? Commented Feb 14, 2017 at 6:04

I don't feel that either one of them has a significantly formal (or casual) tone. (A good rule of thumb is that 漢語 tends to be stilted and formal, while pure-Japanese words are less so.)

One major factor that will affect the formality of those words is their nuance:

  • ずいぶん: implies that the degree is perhaps "too much".
  • 大いに: implies that something was "wholeheartedly" so.

Here is a contrived example of what (I think) that might mean:

  • 「彼はずいぶん意気込んでるね」: "He's...really into it, isn't he?"
  • 「彼は大いに意気込んでる、ね?」: "He's really poured his heart into it, hasn't he?"

Finally, a good neutral semi-formal adjective that is less nuanced is 「非常に」.

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