Be excited, because today's lesson is going to be easy.

The thing is---💀💀💀

[Cue scary sound effects.]

💀 Sudden Quiz of Doom & Despair 💀

Perhaps you know that はやい means "fast."

...and yet it also means "early."

...and it has two different kanji: 速い、早い.

Japanese. Pls. Y u do dis?

Here's the simple explanation:

速い（はやい）
Means "fast" or "speedy."
We use this kanji when something has a high physical speed.

早い（はやい）
Means "early" or "quick."
We use this kanji when something ends or takes place early or in a short amount of time.

Make sense? I hope so, because it's quiz time.

Below we have a few sentences.
You must decide whether the correct kanji for はやい is 速い or 早い.

Go!

❶
俺足はやいよ。
おれ　あし　はやい　よ。

❷
もう終わったの？はやくない？
もう　おわった　の？　はやく　ない？

➌
新幹線はやいね。
しんかんせん　はやい　ね。

...Uh, where are the translations?

Well, that would kind of give away the answers, wouldn't it?

Maybe not, I guess. Here are the sentences with English.

❶
俺足はやいよ。
おれ　あし　はやい　よ。
I can run fast.
Literally: "I (masc.) + legs + fast + よ."

❷
もう終わったの？はやくない？
もう　おわった　の？　はやく　ない？
You're already finished? That was fast.
Literally: "already + finished + の? + not quick?"

➌
新幹線はやいね。
しんかんせん　はやい　ね。
Bullet trains are fast, huh?
Literally: "bullet train + fast + ね."

You know, it's still a little tricky, even with the English translations.

Let's look at which kanji are natural...

❶
俺足速いよ。
おれ　あし　はやい　よ。
I can run fast.
Literally: "I (masc.) + legs + fast + よ."

We are talking about the physical speed at which something moves, so we use 速い.

❷
もう終わったの？早くない？
もう　おわった　の？　はやく　ない？
You're already finished? That was fast.
Literally: "already + finished + の? + not quick?"

We are talking about the amount of time that something took to be completed. Since it was earlier than one would expect, we can say that it was quick. We use the kanji 早い.

Also note that this negative form, 早くない？, just emphasizes the fact that it was fast. In other words, it's a rhetorical question.

➌
新幹線速いね。
しんかんせん　はやい　ね。
Bullet trains are fast, huh?
Literally: "bullet train + fast + ね."

This is actually a trick question. If we're riding in the train looking at the window, then we would use 速い, because we're talking about the physical speed of the train.

But if we are at the station and see that the train has arrived earlier than it was scheduled, then we would use 早い：

新幹線早いね。
しんかんせん　はやい　ね。
The bullet train is early, isn't it?
Literally: "bullet train + early + ね."

Tricky. Tricky.

Oops. This was supposed to be a JLPT lesson! Everything we've looked at so far is mad casual. That simply will not do.

---

JLPT N1: ～が早いか...

This phrase means something like "no sooner did ~ than..." or "the moment that ~, ..."

Let's say the ～ is "our food arrived (at a restaurant)."

Then the ... can be "we all dug in (=started eating vigorously)."

No sooner did our food arrive than we were all digging in.

The moment our food arrived, we all dug in.

In Japanese, we can say:

Our food arrives が早いか we all dug in.

Let's look at a full Japanese sentence:

私たちは料理が運ばれてくるが早いか、勢いよく食べ始めた。
わたしたち　は　りょうり　が　はこばれてくる　がはやいか、　いきおい　よく　たべはじめた。
The moment our food arrived, we all dug in.
Literally: "we + は + food / cooking + が + is brought it (=is carried + comes) + が早いか, + vigorously + started eating."

The important thing to note is that the second half of the sentence is something that happens unexpectedly soon after the first half of the sentence. For this reason, the second half of the sentence will always be something that actually happened/happens.

That is, no requests, commands, conjectures, etc. for the second half of the sentence.

Also, note that the first half of the sentence is in present tense. In fact, it will always be in present plain form (=dictionary form):

V る ＋ が早いか

Examples have always been the best at explaining...

勇太は宿題が終わるが早いか、テレビゲームを始めた。
ゆうた　は　しゅくだい　が　おわる　がはやいか、　テレビゲーム　を　はじめた。
The second Yuta finished his homework, he was already playing video games.
Literally: "Yuta + は + homework + が + finish + が早いか, + video game (=TV game) + を + started."
Note: Or we could just translate this as, "Yuta started playing video games the second he finished his homework."

Just one more, then you're free to forget all of this Japanese...

...unless you want to pass JLPT N1, I guess...

女性の悲鳴が聞こえるが早いか、彼は家を飛び出した。
じょせい　の　ひめい　が　きこえる　がはやいか、　かれ　は　いえ　を　とびだした。
The second he heard the woman's scream, he dashed out of the house.
Literally: "woman / female + の + scream + が + can hear + が早いか, + he + は + house + を + rushed out of / jumped out of."

Now you might be wondering, Do people actually use this Japanese?

I'm pretty sure I've never heard someone use this in spoken Japanese. My grammar books, however, do not say that it is reserved for written language only. So I guess you could say it... but use at your own risk. ^^