Learn Hardcore Chinese: wǒ juéde zǎo shuìjiào shì yí gè hǎo xíguàn. - I think going to bed early is a good habit.

想 (xiǎng)
1. to want to: 我想睡觉。= I want to sleep.
2. to think / to consider: 你怎么想？= What do you think?
  It’s broader and often implies considering or wanting.
认为 (rènwéi)
More formal, often used for more serious or logical judgments:
我认为这个办法很好。= I consider this method good.

In everyday speech about personal feelings/opinions, 觉得 is the most common.

Why is there no word for “that” in “I think that going to bed early is a good habit”? Where would “that” go?

Chinese usually does not use a word like English “that” to introduce a clause.

The pattern is simply:

我觉得 + [a full sentence]

So in:

我觉得早睡觉是一个好习惯。

the part 早睡觉是一个好习惯 is just a full sentence functioning as the object of 觉得, without any extra “that” word.

There is a word “that” in Chinese (“那” / “那个” etc.), but it’s mainly demonstrative (“that one”), not a conjunction introducing clauses in this way.

In 早睡觉, what does 早 (zǎo) do exactly, and why is it before 睡觉 (shuìjiào)?

早 here means “early” and functions like an adverb modifying the verb phrase 睡觉 (“to sleep / go to bed”).

Chinese normally puts adverbs before the verb:

早睡觉 = sleep early / go to bed early
慢走 = walk slowly
经常锻炼 = exercise often

So 早睡觉 literally is “early-sleep”, i.e. “to sleep early”.

What’s the difference between 早睡觉, 早睡, and 睡得早? Can I use them interchangeably?

They are related but used slightly differently:

早睡觉 (zǎo shuìjiào)
- Common in spoken Chinese.
- Emphasizes the action “to go to bed early”.
- Example: 我想养成早睡觉的习惯。
  = I want to develop the habit of going to bed early.
早睡 (zǎo shuì)
- Shorter; often used in writing or in set phrases (e.g. 早睡早起 “sleep early, get up early”).
- Also means “to sleep early / go to bed early”.
睡得早 (shuì de zǎo)
- Uses the 得 structure describing how the action is done.
- More like “sleep early” describing a specific instance or a usual manner.
- Example: 他昨天睡得很早。
  = He went to bed very early yesterday.

In your sentence, 早睡觉是一个好习惯 and 早睡是一个好习惯 are both fine and natural.
睡得早是一个好习惯 sounds a bit less idiomatic, because 睡得早 usually describes how someone sleeps, not the abstract idea as a “habit”.

Why is 睡觉 (shuìjiào) written with two characters? Sometimes I see just 睡, sometimes 睡觉. What’s the difference?

睡 (shuì) means “to sleep” as a verb.
觉 (jiào) originally means “sleep” as a noun.

睡觉 is a verb-object phrase, literally “sleep-sleep”, and is often just translated as “to sleep / to go to bed”.

Usage:

我想睡觉。 = I want to sleep / go to bed.
他在睡觉。 = He is sleeping.

You can also see 睡 alone, especially with additional complements:

睡得很好 = sleep well
他睡了八个小时。 = He slept for eight hours.

In many everyday sentences like “go to bed / sleep”, 睡觉 is the usual way to say it.

What is 是 (shì) doing in 早睡觉是一个好习惯? Can it be left out?

Here 是 is the linking verb “to be”, linking:

Subject: 早睡觉 (going to bed early)
Predicate: 一个好习惯 (a good habit)

So: 早睡觉是一个好习惯。 = “Going to bed early is a good habit.”

In sentences where both sides are nouns or noun phrases, 是 is usually required:

他是老师。= He is a teacher.
这个地方是图书馆。= This place is a library.

You cannot naturally drop 是 here.
✗ 早睡觉一个好习惯 is ungrammatical.

Why do we need 一个 (yí gè) in 一个好习惯? Could we just say 好习惯?

个 (gè) is a measure word (classifier), and 一 (yī/yí) is “one”. Together 一个 is like “one (unit of)”.

一个好习惯 = “a good habit” (literally “one + CL + good habit”).

You can also say simply:

早睡觉是好习惯。

This sounds a bit more general:

with 一个: “(It is) a good habit.”
without 一个: “(It is) good as a habit / (it belongs to the category of) good habits.”

Both are correct; 一个好习惯 is very natural and perhaps a bit more colloquial in this context.

Why is 一 (yī) pronounced “yí” in 一个 (yí gè)?

This is tone sandhi (tone change).

The basic tone of 一 is yī (1st tone), but:

Before a 4th-tone syllable, 一 changes to 2nd tone: yí.
Before a 1st, 2nd, or 3rd tone, it usually changes to 4th tone: yì.

Since 个 (gè) is 4th tone, 一 becomes yí:

一 + 个 → yí gè (一个).

You still write 一, but pronounce yí gè.

Why is there no 的 (de) in 好习惯? Could I say 好的习惯 instead?

Both 好习惯 and 好的习惯 are grammatically correct.

General rule:

When a single-syllable adjective (like 好) modifies a noun, especially in common, abstract, or fixed combinations, 的 is often omitted:
- 好朋友 (good friend)
- 新手机 (new phone)
- 大问题 (big problem)

So 好习惯 is very natural.

好的习惯 is also okay. It can sound a bit more emphatic or formal, or used when the adjective phrase is longer:

非常好的习惯 (a very good habit) — here you must use 的.

Why is the whole phrase 早睡觉 placed at the beginning? Is it acting like a subject?

Yes. In the clause:

早睡觉是一个好习惯。

早睡觉 functions as the subject: the thing you are making a statement about.
So the structure is:

[Subject] + 是 + [Predicate Noun]
早睡觉
- 是 + 一个好习惯

This is similar to English “Going to bed early is a good habit.”, where “Going to bed early” is also a subject.

Then the whole clause 早睡觉是一个好习惯 serves as the object of 我觉得.

Is the sentence saying I personally go to bed early, or just that going to bed early in general is a good habit? Who is the subject of 早睡觉?

早睡觉 here is general; it does not specify who is going to bed early.

The sentence means:

“I think (the practice of) going to bed early is a good habit.”

Chinese often leaves out a specific subject when talking about general truths or general habits. You could interpret it as:

“If people go to bed early, that is a good habit.”

It does not necessarily mean “I go to bed early.” It’s a general statement.

Could I change the word order to 我觉得是一个好习惯早睡觉? Why or why not?

No, 我觉得是一个好习惯早睡觉 is ungrammatical.

Chinese basic structure here is:

我觉得 + [Subject + 是 + Predicate]

So we need to keep:

Subject: 早睡觉
Linking verb: 是
Predicate: 一个好习惯

The natural order is:

我觉得早睡觉是一个好习惯。

You generally cannot split 是 from its subject and then put the subject after the predicate, the way English sometimes moves elements around. Word order is stricter in Chinese.

Can I say 我想早睡觉是一个好习惯 instead of 我觉得早睡觉是一个好习惯?

You could, but it would sound strange, because:

想 before a full sentence often means “to plan / intend / want to”.

我想早睡觉是一个好习惯 is hard to parse and sounds unnatural.

If you want to express “I think…”, 觉得 (everyday) or 认为 (more formal) are better:

我觉得早睡觉是一个好习惯。
我认为早睡觉是一个好习惯。

Use 想 for “want to do something” or “wonder / think about something”, not for this kind of “I think that…” statement.