Learn Hardcore Chinese: Tīngdào tā de shēngyīn, wǒ jiù juéde hěn kāixīn, xīnqíng yě hǎo duō le. - When I hear her voice, I feel very happy, and my mood is much better.

Grammatically, the first part is a time/condition clause (“when/as soon as X happens”), and the second part is the result. Chinese often uses just a comma (no word like “when”) to link these, especially when there’s a word like 就 in the second part to show “then / immediately / as a result”.

What does 就 (jiù) do in “我就觉得很开心”?

就 here shows that the result happens immediately / naturally / directly after the first action:

听到她的声音，我就觉得很开心。
When I hear her voice, I (then / immediately) feel very happy.

Nuances:

If you remove 就:
- 听到她的声音，我觉得很开心。
  Still correct, but feels more neutral.
With 就, it emphasizes:
- quickness: as soon as I hear her voice, I feel happy, and/or
- certainty/inevitability: whenever I hear her voice, I will feel happy.

So 就 is not strictly required grammatically, but it adds a natural, emotional, and temporal connection between the two parts.

Why is 听到 (tīngdào) used instead of just 听 (tīng) or 听见 (tīngjiàn)?

听到 is 听 (to listen/hear) + 到 (result complement “reach/achieve”).

听 alone can mean “to listen” or “to hear” in a general sense.
听到 emphasizes successfully hearing, i.e. the sound has actually reached your ears.
听见 is very similar in meaning to 听到, also “to hear (perceptibly)”.

In this sentence:

听到她的声音 highlights the moment you actually hear her voice.
You could say 听见她的声音 instead; it would sound very natural too.
Just 听她的声音 is possible, but it can sound a bit more like “listen to” (an ongoing action) and less like a specific trigger moment.

So 听到 here matches the idea of “once I hear her voice (successfully, at that moment)” which then triggers the emotional reaction.

What exactly does the 的 (de) in 她的声音 do? Why not just 她声音?

的 is the possessive marker (similar to English “’s” or “of”):

她的声音 = her voice
(literally “she + ’s + voice”)

Without 的:

她声音 is not standard here. You normally need 的 between a pronoun and the noun it possesses.

So:

她的声音 = correct and natural
她声音 = wrong / extremely unnatural in normal Mandarin

Why is it 很开心 instead of just 开心? Does 很 really mean “very” here?

In modern spoken Chinese, 很 before an adjective often does not strongly mean “very”; it’s partly a grammatical softener.

我开心。
Grammatically OK, but often sounds a bit bare or like you’re contradicting something (e.g. “I AM happy (not unhappy)”).
我很开心。
Feels like a normal, neutral statement: I’m (very) happy.

In this sentence:

我就觉得很开心
Reads naturally as “I feel (very) happy”.
The strength of “very” depends on context and tone, but it’s usually not as strong as English “very very”.

So:

很 here has both a bit of meaning (quite/very) and a role of making the adjective phrase sound smooth and natural.

What is the difference between 开心 and 心情, and why are both used?

开心 (kāixīn): an adjective, happy / delighted / in high spirits.
心情 (xīnqíng): a noun, mood / state of mind.

So:

我就觉得很开心 — I then feel very happy (describes the feeling itself).
心情也好多了 — my mood also becomes much better (describes the overall mood/state improving).

Using both makes the emotional change sound fuller and more natural:

First: I feel happy (momentary feeling)
Then: my overall mood is much better (lasting mood).

You could say only one of them, but using both gives a nice, colloquial emphasis.

What does 也 (yě) add in “心情也好多了”? Could we omit it?

也 basically means “also / too / as well”.

It connects “my mood became much better” with the previous statement “I feel very happy”:
- I feel very happy, and my mood is also much better.

Nuance:

With 也:
- 心情也好多了 → “my mood also became much better (in addition to me feeling happy)”.
Without 也:
- 心情好多了 → “my mood became much better.”
  Still correct, but it doesn’t explicitly link to the first clause as “also”.

So 也 highlights that the improvement in mood is another effect of hearing her voice, not a totally separate statement.

What does 多 (duō) do in “好多了”? Why not just 心情也好了?

好多了 is made of:

好 = good
多 = much / many / a lot
了 = change-of-state marker (here)

So 好多了 literally means:

“good by a lot now” → much better / a lot better

Compare:

心情也好了。
My mood is (now) good too.
(Just says the mood is good.)
心情也好多了。
My mood is also much better now.
(Emphasizes improvement from a worse state.)

In the context “I hear her voice and then…”, 好多了 fits very well because it implies that her voice improves your mood significantly.

What is the function of 了 (le) at the end of “心情也好多了”?

Here 了 is a change-of-state 了, not a simple past tense marker.

It signals that the situation has become different from before.
心情也好多了 = “My mood is now much better (than it was before).”

Key points:

It does not just mean “past”; it emphasizes “now it’s changed / now it’s like this”.
Without 了:
- 心情也好多。
  This is grammatically odd and incomplete in this context.
With 了:
- It clearly marks the result of hearing her voice: your mood has shifted to a better state.

So 了 is crucial here for the sense of “has become”.

There is no verb like “become” or “is” in “心情也好多了”. How is this sentence still complete?

In Chinese, adjectives often function as stative verbs on their own.

心情好 literally = “mood good”
→ the mood is good.
心情好了 = “mood (has become) good now”.

So in:

心情也好多了

We can understand it as:

Subject: (我的) 心情 — “(my) mood” (subject “I” is still understood from earlier).
Predicate: 好多了 — “(has become) much better now.”

No extra verb like “是” or “变得” is required in everyday Chinese. The adjective + 了 construction already expresses “has become + adjective”.