Good
“I object to violence because when it appears to do good, the good is only temporary; the evil it does is permanent.” - Mohandas Gandhi
There is one “weird” adjective that doesn’t play well with the rest, and that’s the word “good.”
いい
The thing about this adjective that makes it weird isn’t the conjugation part itself (actually, that part works just fine). The weird thing is the adjective. When you conjugate it, it transforms into another word. Blame that on new and old versions of the same word. Here’s how it goes.
a いい means “good”
a よい also means “good,” though I’d say it’s not as common as いい. It also shares the same kanji, and looks the same when written (良い)
When you conjugate いい to past, negative, or past negative, you have to use the second version of this word (よい). To put it clearly, here’s how you do it:
a いい → Good
a よかった → Was good
a よくない → Not good
a よくなかった → Was not good
See how the adjective transforms to its other version?
This is just something you have to remember as you go along. If you say something like いかった, it just sounds weird (and isn’t right). Luckily, this word is extremely common. When something goes well for someone, you’ll often hear a thankful “よかった！” indicating things went well. That particular word right there deserves to be on the Japanese word hall of fame.
Before you move on, all you need to do is make sure you memorize the conjugations for this one い adjective. It’s only one word, but it’s such an important one I wanted to make it have its own page for you to learn about it.