Forms of "good"

[Tom]

I've learned to use いい for "good," but recently I've seen よい used as well. Do these have the same meaning? Can I use よい any place where I might have used いい, and how would I decide when to use which?

Also, in my textbook, いい is always listed as irregular because it always seems to be conjugated as if it were よい. Does this mean that they are the same word?

[法月]

いい and よい is written the same in kanji as 良い. いい is the deviated form of よい and is very much common in current days. You probably won't see anyone using よい unless you're reading a literature piece.

They essentially mean the same thing, but よい is no longer use in typical speech. However, a form of よい is still used when conjugated to negative form, 良くない, you must use よくない and not 「いいくない」 or 「いくない」.
Some people have been using 「いいくない」 or 「いくない」 in Japanese speech, but it is still not accepted as Japanese language standards.

[Tom]

Thanks!

[jkid]

Some people have been using 「いいくない」 or 「いくない」 in Japanese speech, but it is still not accepted as Japanese language standards.

Thanks for the tip!