What is the origin and usage of the word いい?


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?




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.




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.

