i-adjective
Describes high speed of movement, action, or change. 速い is the typical kanji for physical speed, but 早い is also used.
彼は走るのが速い。
He runs fast.
このパソコンは処理が速い。
This computer processes quickly.
i-adjective
premature; too soon; too early
Only when written 早い
Indicates that something happens before it is appropriate or desirable. Often used in negative contexts. Written with 早い.
まだ10時だ。帰るには早すぎる。
It's only 10 o'clock. It's too early to go home.
彼の死は早すぎた。
His death was premature.
i-adjective
Used when a task can be completed quickly because it is not difficult. Often in the pattern ~するのが早い. Typically written with 早い.
この問題は解くのが早い。
This problem is quick to solve.
彼は決断が早い。
He is quick to make decisions.
i-adjective
as soon as; the moment; the instant
Used in the grammatical patterns ~するが早いか and ~するより早く to mean 'no sooner than' or 'the moment something happens'. Literary and somewhat formal.
彼は家に着くが早いか、また出かけた。
The moment he arrived home, he went out again.
言うより早く、彼は走り出した。
No sooner said than done, he started running.