Learn Hardcore Japanese: hayaku okinakereba, gakkou ni maniaimasen. - If I don't wake up early, I won't be on time for school.

早い is an い-adjective meaning “early” or “fast.” To modify the verb 起きる, you need the adverbial form, which you get by replacing い with く. Thus 早く起きる means “to wake up early.”

What exactly does 起きなければ mean in this sentence?

This is the negative conditional form of 起きる (“to wake up”). You start with the plain negative 起きない, drop ない, and add なければ, giving 起きなければ, literally “if (I) don’t wake up.” It sets up the “if” clause that leads to the result in the second half.

Why is the particle に used after 学校 in 学校に間に合いません?

The verb 間に合う (“to be in time for, to make it”) takes its target with に. So 学校に間に合う = “make it to school on time.” The negative 間に合いません simply means “won’t make it (on time).”

Could I say this more casually, for example with 〜ないと or 〜なきゃ?

Yes. Both are common in spoken Japanese:
• 早く起きないと学校に間に合わない。
• 早く起きなきゃ学校に間に合わない。
They mean the same “If I don’t wake up early, I won’t make it to school on time,” but sound less formal than なければ…ません.

Why is there no subject like 私は in the sentence?

Japanese often omits the subject when it’s clear from context. Here it’s obvious the speaker is talking about themselves, so 私は isn’t needed.

What’s the nuance between 間に合う and 遅れる?

• 間に合う emphasizes arriving on time or making the deadline.
• 遅れる means to be late.
Saying 間に合いません stresses that you simply won’t make it at all, rather than just being a little late.

Why does the sentence just use a comma after 起きなければ instead of adding ので or から?

In Japanese, conditional clauses (like …なければ) are frequently linked to their result clauses with just a comma. The cause-and-effect relationship is clear without extra conjunctions, making the sentence more concise and natural.