Learn Hardcore Chinese: suīrán tā hěn máng, dànshì tā yídìng huì lái. - Although he is very busy, he will definitely come.

In Chinese it’s very natural to use both: 虽然…, 但是… (“although…, but…”). You can drop 但是 and say 虽然他很忙，他一定会来。 and it’s still fine. But don’t use 虽然 alone with no contrasting result, and don’t put 但是 in the first clause.

Why is there 很 before 忙? Does it always mean “very”?

Predicative adjectives in Chinese usually need a degree marker, and 很 often functions as a neutral linker, not necessarily “very.” So 他很忙 is the normal way to say “he is busy.” 他忙 is possible but sounds more emphatic or specific (e.g., answering “Is he busy?”).

What does 会 mean here?

会 here expresses likelihood/future prediction (“will”). It’s not the “can/know how to” meaning. So 他一定会来 = “He will definitely come.”

Where should 一定 go relative to 会?

Put the adverb 一定 before the modal 会: 他一定会来. Forms like 他会一定来 are unnatural.

Can I omit 会 and just say 他一定来?

Without a time word or particle, 他一定来 sounds odd. You can either keep 会 (他一定会来) or add a future time: 明天他一定来, or use a sentence-final particle: 他一定来的。 For simple prediction, 会 is the safest.

Can I use 要 or 能 instead of 会?

要 indicates plan/intent or obligation. 他一定要来 = “He must/insists on coming,” not a neutral prediction.
能 is about ability/possibility. 他一定能来 = “He will definitely be able to come.”
For “will (very likely),” stick with 会.

Do I need to repeat 他 after 但是?

No. If the subject is the same, you can omit it in the second clause: 虽然他很忙，但是一定会来。 You can also omit it in the first clause if context is clear: 虽然很忙，但是他一定会来。

Can I replace 但是 with 可是 or 不过? Any nuance differences?

Yes:

但是: neutral to slightly formal.
可是: more colloquial.
不过: “however,” softer contrast.
All work with 虽然, e.g., 虽然他很忙，可是/但是/不过他一定会来。

Can I replace 虽然 with 尽管?

Yes. 尽管 ≈ “although,” slightly more formal/forceful. 尽管他很忙，他一定会来。 Note 尽管 can also mean “feel free to” in other contexts.

Can I put 虽然 in the second clause or reverse the order?

No. 虽然-clauses typically come first. Don’t say 他一定会来，虽然他很忙. If you want the main clause first, use a different connector: 他很忙，不过他一定会来。

How strong is 一定? Is it 100% certain?

一定 signals strong speaker confidence (“definitely/for sure”), but in real life it’s not absolute 100%. Near-synonyms: 肯定 (can be adverb or verb; a bit more “I’m sure”), 必定/必然 (formal, “inevitably”).

What’s the full pinyin and any tone changes I should know?

Pinyin: suīrán tā hěn máng, dànshì tā yídìng huì lái.
Tone sandhi: 一 in 一定 becomes second tone (yí) before a fourth-tone syllable (dìng). Everything else is as written.

Why is there a comma in the middle?

Chinese uses a comma to separate the concessive clause from the main clause: 虽然…, 但是…. It marks a natural pause and the contrast.

Could I add 还是 to show “still”?

Yes: 虽然他很忙，他还是会来。 还是 highlights “still” in spite of the first clause. It can replace or accompany connectors like 但是 (but don’t stack too many at once).

Can I add 的 at the end for emphasis?

Yes. 他一定会来的。 The sentence-final 的 adds assurance/soft emphasis, often used to comfort or reassure someone.