Learn Hardcore Chinese: tā juéde shìjiè shàng de hěnduō chéngshì dōu hěn yǒuyìsi. - She thinks many cities in the world are very interesting.

世界上的很多城市 (most natural)
- The unit 世界上的 tightly modifies 城市.
- Roughly: “the many cities (that are) in the world”.
- Feels like we first define “cities in the world”, then say “many (of them)”.
世界上很多城市
- No 的; this is also correct and common.
- Roughly: “many cities in the world”, with 世界上 as a looser location phrase.
很多世界上的城市
- Grammatically possible but sounds awkward and not idiomatic.
- It makes 很多 modify 世界上的城市 as one whole chunk, which is not how people usually say it.

So in ordinary speech/writing, 世界上的很多城市 or 世界上很多城市 are preferred; 很多世界上的城市 is rarely used.

What does 都 mean here, and why is it used with 很多 (“many”)?

都 basically marks “all (of them)” or “as a whole”.

In 世界上的很多城市都很有意思:

很多城市 = many cities
都 = treating those many cities as a set and saying “they all (as a group) are interesting”

It does not mean literally every city in the world. It means:

Among the many cities (that we’re talking about), they are all interesting.

So the logic is:

pick a subset: 很多城市 (many cities)
then 都 = all of those in that subset share the property 很有意思.

That’s why 都 can co‑occur with 很多, 一些, 几个, etc.:

这几个地方都很好玩。
These few places are all fun.

Could we leave 都 out? What changes if we say 世界上的很多城市很有意思?

You can say 世界上的很多城市很有意思, and it is grammatical.

The nuance:

With 都:
世界上的很多城市都很有意思。
⇒ More strongly emphasizes that each of those many cities is interesting, taken one by one.
Without 都:
世界上的很多城市很有意思。
⇒ Feels more like a general statement: “many cities in the world are interesting” (less emphasis on “each of them”).

Both are fine; 都 just adds that “all of the ones we’re talking about” feeling.

Why is there 很 before 有意思? Can we say 都有意思?

In modern Mandarin, adjectives usually need a degree adverb like 很 in simple descriptive sentences.

很有意思 = “very interesting”, but in many contexts 很 is a bit like a neutral linker, not always a strong “very”.

Compare:

这个城市很有意思。 ✅ (normal)
这个城市有意思。
– can be okay in some contexts, but as a neutral description it may sound a bit bare or more emphatic/unusual.

In this sentence, 都很有意思 is the most natural:

都有意思 is not wrong, but it’s less typical as a neutral statement. Learners are safer including 很 before most predicate adjectives in such sentences.

Why is there no 是 before 很有意思? Why not 都是很有意思?

In Chinese, adjectives (like 有意思, 漂亮, 大) function as stative verbs. They don’t need 是 when used as predicates:

城市很有意思。 = “Cities are interesting.”
(literally: “cities very-interesting”)

If you add 是:

城市是很有意思的。
– This has a different feel: often used for contrast or emphasis, like “(Indeed) cities are interesting (at least in that respect).”

So:

都很有意思 = normal, neutral statement.
都是很有意思的 = emphatic or contrastive, not wrong but different in tone.

For basic descriptive sentences, drop 是 before an adjective predicate.

What’s the difference between 觉得, 想, and 认为 here?

All three can relate to thinking, but their usage is different:

觉得
- Most common for personal feelings, opinions, impressions.
- Matches “feel / think” in everyday speech.
- 她觉得世界上的很多城市都很有意思。
  ⇒ She feels / thinks many cities in the world are interesting.
想
- Core meaning: to want / to intend / to think (about).
- If you replace 觉得 with 想 here:
  她想世界上的很多城市都很有意思。 ❌
  – sounds wrong; 想 in this pattern usually needs another verb or a complement (e.g. 她想去很多城市, she wants to go to many cities).
认为
- More formal, like “to consider / to be of the opinion that”.
- 她认为世界上的很多城市都很有意思。
  ⇒ More formal or academic tone than 觉得.

So 觉得 is the natural, everyday choice in this sentence.

Why don’t we say 城市们 to show the plural, like “cities”?

Chinese usually does not use a plural suffix for inanimate nouns.

们 is mainly for:
- people: 我们, 他们, 学生们
- sometimes animals, in special contexts.

For things like 城市, 书, 桌子, plural is usually shown by:

a number: 三个城市 (three cities)
a quantifier: 很多城市 (many cities)
context only

So 城市们 is almost always wrong or at least very strange; 很多城市 already clearly means “many cities” without 们.

Why do we say 世界上的很多城市 and not 在世界上的很多城市?

Both patterns exist but they function differently:

世界上的很多城市
- 世界上的 is an attributive phrase directly modifying 城市.
- Literally: “(the) many cities that are in the world”.
- It’s a noun phrase.
在世界上的很多城市
- 在 makes it a location phrase, usually modifying an action:
  - 在世界上的很多城市都说英语。
    ⇒ In many cities in the world, people speak English.
- This structure expects some verb/action after it: 在世界上的很多城市 + (do something).

In your sentence, the subject is simply the noun phrase 世界上的很多城市, so 在 is not needed.

Could we say 世界上很多城市都很有意思 without the 的? Is there a difference?

Yes, 世界上很多城市都很有意思 is also correct and common.

Nuance:

世界上很多城市都很有意思。
⇒ 世界上 is a location phrase, and 很多城市 is the subject. Very natural.
世界上的很多城市都很有意思。
⇒ Slightly more “tightly packaged” as “the many cities (that are) in the world”.
The 的 binds 世界上 more directly to 城市.

In everyday spoken Chinese, both versions are widely used; the difference is subtle and doesn’t affect the basic meaning.

Where exactly should 都 go in the sentence? Could we move it?

Basic rule: 都 comes after the subject and before the predicate (verb/adjective).

In this sentence:

Subject: 世界上的很多城市
Predicate: 很有意思

So the correct placement is:

世界上的很多城市都很有意思。 ✅

Examples of wrong or unnatural positions:

都世界上的很多城市很有意思。 ❌
世界上的很多城市很都有意思。 ❌

When you have a subject like 他们, 这些人, 很多地方, 都 usually directly follows it:

他们都很忙。
这些地方都很好玩。
很多国家都说英语。

Is 有意思 always positive “interesting”? Can it be negative or sarcastic?

Normally:

有意思 = “interesting / fun / enjoyable” (positive)
很有意思 = “very interesting / really fun” (clearly positive)

But in some contexts or with certain tones, it can be used ironically or sarcastically, a bit like English “oh, that’s interesting…” meaning “that’s suspicious / that’s not so good”:

你这样做很有意思啊。 (sarcastic tone)
⇒ “The way you’re doing this is really something, huh.” (implying criticism)

In your sentence, without any special tone markers, 很有意思 should be taken as straightforwardly positive.

How would we change the sentence to mean “She has always thought that many cities in the world are interesting”?

Chinese often leaves tense to context, but if you want to show ongoing / continuous feeling clearly, you can add 一直:

她一直觉得世界上的很多城市都很有意思。
⇒ She has always thought / has consistently felt that many cities in the world are very interesting.

Here:

一直 = continuously, all along
The rest of the structure stays the same.