Why ī is the only romaji that can be spelled as a double ii


I am learning Japanese, and need to enter romaji into my keyboard to enter
Japanese into documents and tables on my smartphone.

My textbook shows ī as the only romaji that can be spelled as a double ii.

[![romahi long
vowels](https://i.stack.imgur.com/kezUa.jpg)](https://i.stack.imgur.com/kezUa.jpg)

Is this a commonplace romaji writing convention, and if so, then why is this?

EDIT:

Would I be right in saying that it is because the alphabetical combinations いい
occur in Japanese (words), whereas ああ, うう, ええ, おお do not?




Hepburn originally transcribed `いい` as `ī`, but in later editions he changed
it to `ii`. Unfortunately, his book doesn't explain why he made this decision,
so I can't say with certainty what the reason was.

I think one reason is most obvious and likely, however: `ī` looks very similar
to `i`, and writing `ii` avoids confusing the two. This isn't a problem for
`a`, `u`, `e`, or `o` because they don't normally have dots over them, so
they're visually distinct from `ā`, `ū`, `ē`, `ō`.

Note that Hepburn did not make the distinction mentioned in Eiríkr Útlendi's
comment; he transcribed `いい` in all cases as `ii`. Although a few people do
make that distinction, it's not common to do so, and you don't have to worry
about it as a learner.

You wrote:

> Would I be right in saying that it is because the alphabetical combinations
> いい occur in Japanese (words), whereas ああ, うう, ええ, おお do not?

No. We can find all five kana sequences in Japanese words. The easiest
examples for the rest are interjections: `ああ`, `ううん`, `ええ`, and `おお`.
Interjections aside, `ああ` is also an adverb, and `おお` appears in a number of
words such as `おおい` and `おおげさ`. We can find more examples if we include
sequences that cross morpheme boundaries, such as `ええん` (会厭) and `ふうう` (風雨).

If you intended to include examples where a long vowel follows a consonant
(although these are technically excluded by what you wrote), we can find more
examples rather easily: `おかあさん`, `ずうずうしい`, `おねえさん`, and `ほのお`.

The explanation in your edit doesn't really make sense.




Hepburn originally transcribed `いい` as `ī`, but in later editions he changed
it to `ii`. Unfortunately, his book doesn't explain why he made this decision,
so I can't say with certainty what the reason was.

I think one reason is most obvious and likely, however: `ī` looks very similar
to `i`, and writing `ii` avoids confusing the two. This isn't a problem for
`a`, `u`, `e`, or `o` because they don't normally have dots over them, so
they're visually distinct from `ā`, `ū`, `ē`, `ō`.

Note that Hepburn did not make the distinction mentioned in Eiríkr Útlendi's
comment; he transcribed `いい` in all cases as `ii`. Although a few people do
make that distinction, it's not common to do so, and you don't have to worry
about it as a learner.

You wrote:

> Would I be right in saying that it is because the alphabetical combinations
> いい occur in Japanese (words), whereas ああ, うう, ええ, おお do not?

No. We can find all five kana sequences in Japanese words. The easiest
examples for the rest are interjections: `ああ`, `ううん`, `ええ`, and `おお`.
Interjections aside, `ああ` is also an adverb, and `おお` appears in a number of
words such as `おおい` and `おおげさ`. We can find more examples if we include
sequences that cross morpheme boundaries, such as `ええん` (会厭) and `ふうう` (風雨).

If you intended to include examples where a long vowel follows a consonant
(although these are technically excluded by what you wrote), we can find more
examples rather easily: `おかあさん`, `ずうずうしい`, `おねえさん`, and `ほのお`.

The explanation in your edit doesn't really make sense.

