Learn Hardcore Japanese: asita ha hayaku kaereru to omoimasu.

Using は with a time word like 明日 is very common when you’re contrasting it with other times (e.g., Today I can’t go home early, but as for tomorrow…), or just when you want to make tomorrow the frame of what you’re talking about.

You could also say 明日早く帰れると思います (without は). That is still understandable, but it sounds a bit more like you just listed 明日 as one of several pieces of information, without highlighting it as the main topic. With は, 明日 feels slightly more “in focus.”

Where is the word I in this sentence? Why is it not written?

Japanese often omits the subject when it’s clear from context.

In 明日は早く帰れると思います, the default interpretation is:

(私は) 明日は早く帰れると思います。
= (I) think I can go home early tomorrow.

私は (I + topic marker) is not written because:

The verb 思います (think) naturally suggests it’s the speaker’s thought.
The action 帰れる (can go home) also naturally fits the speaker unless context clearly points to someone else.

So you don’t need to say 私 unless you want to emphasize it or avoid ambiguity. This kind of omission is completely normal in Japanese.

Why is it 早く and not 早い?

早い is an i-adjective meaning early (or fast in some contexts).
To modify a verb, you usually use the -く form (the adverbial form):

早い → 早く

So:

早く帰る / 早く帰れる = to go home early / to be able to go home early
You cannot say ✕早い帰れる.

Here, 早く is modifying 帰れる, so it must be the adverb form.

Note: There is also 速い / 速く, which focuses more on speed (fast).
For “early” in a time sense (leave early, get up early), 早く is the usual choice. Context tells you whether it means early or fast; in this sentence, it clearly means early (in the day), not going home quickly.

What exactly does 帰れる mean? How is it different from 帰る or 帰ることができる?

帰れる is the potential form of 帰る.

帰る = to go home
帰れる = to be able to go home / can go home

So:

明日は早く帰る
= Tomorrow, I will go home early. (stating what you will do)
明日は早く帰れる
= Tomorrow, I can go home early / I’ll be able to go home early.
(focusing on the possibility/ability, e.g., your work ends early, or you have permission)

帰ることができる also means can go home, but:

帰れる is shorter and more natural in everyday spoken Japanese.
帰ることができる sounds more formal or written, good for official explanations, speeches, etc.

So in casual or normal polite conversation, 帰れる is usually preferred.

Why is 帰れる in the plain form, while 思います is in the polite form?

This is a very important pattern in Japanese:

In sentences with と思います, the part before と is usually in the plain form, even if the overall sentence is polite.

So:

(plain) 帰れる + と + (polite) 思います
明日は早く帰れると思います。

Using 帰れますと思います is unnatural in normal Japanese.
The politeness of the whole sentence is carried by the last verb (思います). Subordinate clauses (like the part before と) are typically in the plain form when you speak politely.

You do the same with other predicates:

高いと思います。 (not 高いですと思います)
行くと思います。 (not 行きますと思います)
雨だと思います。

So: plain before と, then polite at the end is the standard pattern here.

What is the role of と in 帰れると思います?

Here, と is the quotative particle. It marks what is being thought or said.

Structure:

[clause in plain form] + と + 思います
= I think (that) [clause].

In this sentence:

早く帰れる = the content of the thought
と = “that” (connecting content to the verb 思います)
思います = think

So it works just like in:

「行きます」と言いました。
= He said, “I will go.”
行くと思います。
= I think (that) I will go.

You don’t usually translate と as a separate word, but it is grammatically very important: it marks the quoted / thought content.

Can I say the sentence without は, like 明日早く帰れると思います? What’s the difference?

Yes, 明日早く帰れると思います is grammatical and understandable.

The nuance difference is subtle:

明日は早く帰れると思います。
- 明日 is the topic.
- Feels like As for tomorrow, I think I can go home early.
- Slightly more contrastive: maybe today you can’t, but tomorrow you can.
明日早く帰れると思います。
- Just lists 明日 as a time adverbial, without topicalizing it.
- Feels more like a simple factual statement: Tomorrow I think I can go home early.

In conversation, both are fine.
Using は is especially natural if you are contrasting tomorrow with other days or shifting the topic to “tomorrow.”

Can I say 明日は早く帰ると思います instead of 明日は早く帰れると思います? Are they different?

You can say 明日は早く帰ると思います, and it is grammatically correct, but the nuance changes:

明日は早く帰ると思います。
= I think I will go home early tomorrow.
- Focuses on your own future action/plan.
- It sounds like your will or decision.
明日は早く帰れると思います。
= I think I can / will be able to go home early tomorrow.
- Focuses on possibility or conditions (schedule, workload, permission, etc.).
- Suggests: If everything goes as expected, I’ll be able to leave early.

To a boss or coworker, 帰れると思います is often more appropriate, because it sounds like you are talking about whether circumstances allow it, not just stating your own intention.

Does と思います always literally mean I think? Is it very tentative?

と思います often translates as I think (that...), but in Japanese it can be less tentative and also acts as a politeness softener.

Depending on context, ～と思います can feel like:

I think…
I believe…
I suppose…
I’d say… / I’d guess…

Japanese speakers frequently use と思います even when they’re fairly confident, to avoid sounding too blunt. So:

明日は早く帰れると思います。
doesn’t necessarily mean I’m really not sure.
It can mean something like:
I expect I’ll be able to go home early tomorrow (said in a polite, slightly softened way).

Could this sentence also mean I think you can go home early tomorrow instead of I think I can go home early tomorrow?

Yes, in the right context, it could.

Japanese omits subjects, so 明日は早く帰れると思います literally just says:

Tomorrow, (someone) can go home early, I think.

Who that “someone” is depends on context:

If you are talking about your own schedule, it means I.
If you and a coworker are discussing their schedule, it might mean you (or that coworker).

To make it explicit, you can add a subject:

私は明日は早く帰れると思います。
= I think I can go home early tomorrow.
田中さんは明日早く帰れると思います。
= I think Tanaka can go home early tomorrow.

Using あなた is often avoided in workplace conversation; people usually use the person’s name + さん or just rely on context.

Does Japanese have a future tense? Why can this present form talk about tomorrow?

Japanese does not have a separate future tense like English.

The non-past form (dictionary form / ます-form) can express:

present time
future time
general truths / habits

So 帰れる can be:

can go home (in general / now)
will be able to go home (in the future)

The time reference comes from context and time expressions like 明日 (tomorrow). So:

明日は早く帰れると思います。
= I think I can go home early *tomorrow.*

Even though the verb is not “future tense,” 明日 tells you it’s about the future.

Is 明日は早く帰れると思います normally written with spaces?

No. In standard Japanese writing, you don’t put spaces between words like in English.

The natural way to write it is:

明日は早く帰れると思います。

Spaces are often added in textbooks or teaching materials to help learners see the word boundaries:

明日｜は｜早く｜帰れる｜と｜思います。

But in real Japanese texts (emails, messages, books, etc.), you generally write it as one continuous string of characters, with punctuation like 、 and 。 instead of spaces.