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According to Denshi Jisho, [いい and
よい](http://jisho.org/words/?jap=ii&eng=&dict=edict) share the same kanji, and
that both roughly mean "good". Why are there two different pronunciations
despite the similarity, and what are some ways to figure out which one to use?
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2011-06-03T00:50:05.930
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word-choice etymology
What is the origin and usage of the word いい?
i believe that よい is the more polite form of いい. But it coudl also just be an
ease of pronunciation thing that they are different.
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2011-06-03T01:25:58.173
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I am not sure about the origin, but the difference in usage is you can use よい
as another forms よくない、よかった、... but いい normally cannot in Standard Japanese.
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2011-06-03T01:29:33.823
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The [conjugation of
いい](http://www.guidetojapanese.org/learn/grammar/adjectives#part4) is
instructive here. If you want to use the past tense, the conjugation is よかった.
You can't say いかった to mean "was good". Furthermore, the first item in
[goo](http://dictionary.goo.ne.jp/leaf/jn2/9174/m0u/%3044%3044/) confirms that
they have the same meaning.

[goo](http://dictionary.goo.ne.jp/leaf/thsrs/15554/m0u/%E3%81%84%E3%81%84/)
also says that よい is the original word, but いい came about because it's easier
to say. So I imagine it's a kind of slang from a long time ago that has simply
grown to be acceptable.
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2011-06-03T01:38:20.180
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For what it's worth:

よい is an i-adjective and can then be modified like any other adjectives in い

いい is an adjective that can be used as:

- **attributive** :

->That's an _interesting_ idea.

- **predicative** :

->That idea is _interesting_.

Thus like any -ing adjectives cannot be modified.

Origin:

ii and yoi use the same kanji but are usually written in kana. Origin of 好い 善い
良い is obviously Chinese with different nuances for each of them.
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2011-06-03T06:59:31.297
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The original form is definitely よい, and that's what you'll find in old texts.
As often happens with common words, the pronunciation was simplified a little
in its most common form, the Rentaikei form (which is the dictionary form),
and became ええ in western dialects (Kansai-ben) and いい in the Tokyo dialect,
which serves the basis for Standard Japanese.

Today, いい is no longer considered colloquial, and it can easily be found in
formal speech or writing, alongside 良い (よい). It is actually 良い which is now
considered formal-only, and its effectively gone in everyday speech, and
replaced entirely by いい in the Rentaikei, while all other forms are still
conjugated as if the base form was よい.
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2011-06-03T08:24:17.257
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