Learn Hardcore Chinese: tā hěn rènzhēn de xuéxí, xiàwǔ cái hē chá. - He studies very seriously; he only drinks tea in the afternoon.

地 (de) here turns an adjective/adjective phrase into an adverbial to modify the verb: 认真地学习 = “study diligently.”
It’s pronounced “de” with a neutral tone (not “dì,” which means “earth/ground”).

How do 的 / 地 / 得 differ?

的 (de): links modifiers to nouns. Example: 认真的学生 “a diligent student.”
地 (de): marks adverbials before verbs. Example: 认真地学习 “study diligently.”
得 (de): introduces complements after verbs/adjectives. Example: 学习得很认真 “studies very diligently.”

Is 地 required? Is 认真学习 also correct?

认真学习 is fine, especially in speech. 认真地学习 is a bit more formal/explicit.
With an intensifier, both are common: 很认真学习 and 很认真地学习.

Why is 很 there? Does it mean “very,” or is it just a linker?

Here 很 really means “very/to a high degree.” It’s not the “structural 很” used to smooth bare adjectives in predicate position.
Without it: 他认真地学习 = “He studies conscientiously” (neutral degree).
With it: 他很认真地学习 = stronger emphasis. You could also use 非常/十分/挺.

Can I say 他学习得很认真 instead? Any difference?

Yes. 他学习得很认真 uses the “V + 得 + complement” pattern and is fully natural; meaning is essentially the same.
Colloquially you’ll also hear 他学习很认真 (without 得), which is acceptable in speech.

Where does 才 go? Can I move it around?

Standard placement: before the verb it modifies. Examples:
- 他下午才喝茶。
- 下午他才喝茶。
Avoid: 他才下午喝茶 (awkward) or splitting it from the verb.

What nuance does 才 add compared with 就 or 然后?

才: later-than-expected or “not until.” 下午才喝茶 = “not until the afternoon does he drink tea.”
就: earlier/easier-than-expected. 下午就喝茶 suggests “as early as the afternoon.”
然后: simple sequence, no expectation. …，然后喝茶 = “…, and then (after that) drink tea.”

Does 才 mean “only” or “not until”? How is it different from 只?

With times, 才 = “not until” (later-than-expected).
With amounts, 才 implies “only (and that’s fewer/less than expected).” Example: 他才喝了一杯茶 = “He drank only one cup (surprisingly few).”
只 is neutral “only/just,” without the built-in expectation: 他只喝了一杯茶 (just one; no lateness/insufficiency implied).

Is there a cause-effect between the two clauses, or just sequence?

Mostly sequence or mild implication. 他很认真地学习，下午才喝茶 reads as “He studies diligently, and (not until) the afternoon does he drink tea.”
It’s not the strict conditional pattern 只有…才… (“only if … then …”).

Why is there no 了? When would I add it?

No 了 = general/habitual statement or a neutral narration.
For a specific past event: add 了 to the verb: 他今天很认真地学习，下午才喝了茶 (“only in the afternoon did he finally drink tea”).

Is 学习 a verb or a noun here? Could I use 学 or 读书?

Here 学习 is a verb (“to study/learn”). It can also be a noun (“learning/studies”) in other contexts.
学 (to study/learn) also works: 他很认真地学 (a bit terser).
读书 can mean “to study” or “to read books/be in school,” slightly different nuance.

Can I add the progressive marker 在/正在?

Yes: 他正在认真地学习，下午才喝茶。 or 他在认真地学习…
Keep 在/正在 directly before the verb phrase; don’t say 他很认真地在学习 (sounds off). Prefer 他在/正在认真地学习.

Why is there a comma? Could I use a connector?

Chinese often links related clauses with a comma.
You could add 然后 for explicit sequence: 他早上很认真地学习，然后下午才喝茶. With 才, the sense of “only then/later than expected” remains.

Do I need a measure word with 茶? When would I use one?

Can the subject be repeated in the second clause?

It’s optional. The subject 他 is understood after the comma. You can repeat it: 他很认真地学习，他下午才喝茶, but it’s heavier in style.

What if I mean “He only drinks tea (not coffee) in the afternoon,” not “not until the afternoon”?

Use 只 for exclusivity of choice rather than timing: 他下午只喝茶 = “In the afternoon he drinks only tea (no other drinks).”
他下午才喝茶 focuses on the lateness/time threshold, not on excluding other beverages.