要不是……(就 / 早就……): had it not been for…
【高55】连词 / conjunctions
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
要不是 + real fact, (S) + 就 / 早就 / 也不会 + result: you take away a fact that is already settled to say what would have happened without it: "if it weren't for…", "had it not been for…". 要不是老师帮我，我也不能写好这篇文章.
The fact after 要不是 is true (the teacher really did help); the main clause gives the opposite outcome to what happened, often with 就, 早就 or 也不会 (要不是你提醒，我早就忘了).
It only works for settled facts: for a future possibility say 如果不……. And unlike 要不然 / 否则 (hsk4-g10), which open the second clause (你提醒了我，要不然我早就忘了), 要不是 opens the first. Register: neutral, in speech and in writing.
Examples
要不是你提醒我，我早就忘了。
Yàobúshì nǐ tíxǐng wǒ, wǒ zǎojiù wàng le.If you hadn't reminded me, I would have forgotten long ago.
要不是路上堵车，我们早就到了。
Yàobúshì lùshang dǔchē, wǒmen zǎojiù dào le.If it weren't for the traffic jam, we would have arrived long ago.
要不是老师帮我，我也不能写好这篇文章。
Yàobúshì lǎoshī bāng wǒ, wǒ yě bù néng xiěhǎo zhè piān wénzhāng.Without my teacher's help, I could not have written this article well.
要不是他推迟回国，也不会赶不上面试。
Yàobúshì tā tuīchí huíguó, yě bú huì gǎn bu shàng miànshì.Had he not put off his return, he would not have missed the interview.
要不是有这笔奖学金，他恐怕连大学都读不完。
Yàobúshì yǒu zhè bǐ jiǎngxuéjīn, tā kǒngpà lián dàxué dōu dú bu wán.Without this scholarship he probably could not even have finished university.
要不是一位同事帮我备份了记录，这些数据早就被系统清除了。
Yàobúshì yí wèi tóngshì bāng wǒ bèifèn le jìlù, zhèxiē shùjù zǎojiù bèi xìtǒng qīngchú le.If a colleague hadn't backed up the records for me, the system would long since have wiped this data.
Common mistakes
✗ 要不是下雨，我们明天去爬山。 → ✓ 如果不下雨，我们明天去爬山。 (a future possibility is not a settled fact).
✗ 要不是你帮忙，我完成了这个任务。 → ✓ 要不是你帮忙，我不可能完成这个任务。 (the main clause says what would not have happened; it does not repeat what did happen).