Learn Hardcore Japanese: kyou ha zangyou ga nai node, hayaku kaerimasu. - Since I don't have overtime today, I will go home early.

Without は, you could still say 今日、残業がないので、早く帰ります, and it’s understandable, but 今日は feels more like “today in particular” or “at least for today,” which is natural in this context.

Why is が used after 残業 (in 残業がない), and not は?

が is marking 残業 (“overtime”) as the subject of the verb ない (“does not exist / there is not”).

The structure is:

残業がある = There is overtime.
残業がない = There is no overtime.

In sentences expressing existence or non‑existence (“there is / there isn’t X”), the thing that exists is usually marked by が.

If you said 残業はない, it would be more contrastive, like:

(他の仕事はあるけど) 残業はない。
“(There’s other work, but) as for overtime, there isn’t any.”

In this simple, neutral statement of “there is no overtime,” 残業がない with が is the most natural.

Why is it 残業がない and not 残業がありません? Is it okay to mix ない with 帰ります (plain + polite)?

Yes, it’s okay, and it’s very common.

ない is the plain negative form.
ありません is the polite negative form of あります.

So:

残業がないので、早く帰ります。
残業がありませんので、早く帰ります。

Both are grammatically correct.

Using ない in the subordinate clause (…ので) and 帰ります (polite) in the main clause is a normal pattern in spoken Japanese. Many speakers drop to plain form inside the reason clause, especially with very common words like ある／ない.

If you want to sound more formal (e.g., in writing or in a very polite work context), 残業がありませんので、早く帰ります may feel slightly more polished. In everyday speech, 残業がないので… is completely natural.

What is the nuance difference between 残業がない and something like 残業をしません?

They’re close in meaning but not identical.

残業がない
Literally: “There is no overtime.”
→ Focuses on the situation: your workplace simply does not have overtime scheduled today.
残業をしません
Literally: “(I) will not do overtime.”
→ Focuses on your action or decision: you are not going to do overtime (even if overtime might exist as an option).

In the given sentence, the idea is “today, overtime just doesn’t exist / isn’t scheduled,” so 残業がない is the more natural choice.

What exactly does ので mean here, and how is it different from から?

Both ので and から can mean “because / since.”

In this sentence:

残業がないので、早く帰ります。
“…so / because there is no overtime, I’ll go home early.”

General nuance (very broadly):

ので
- Feels a bit more formal, soft, or explanatory.
- Often used when you’re giving a reason in a relatively polite or neutral way.
から
- Slightly more direct and a bit more casual in many contexts.
- Also completely fine here: 残業がないから、早く帰ります。

In everyday speech both are widely used; ので just fits nicely with the polite 帰ります and gives a gentle, explanatory tone.

Why is it 早く and not 早い before 帰ります?

早い is an adjective (“early / fast”).
To turn many -い adjectives into an adverb (“early-ly / quickly”), you change -い to -く:

早い → 早く
高い (“high”) → 高く (“highly”)
遅い (“late / slow”) → 遅く (“late / slowly”)

So:

早く帰ります。 = “(I will) go home early.”

You can’t say 早い帰ります; verbs need an adverb-like form (早く) modifying them, not the plain adjective form.

Why is the verb 帰ります used instead of 行きます for “go home”?

In Japanese:

行く = “to go” (in general, to move away toward some place)
帰る = “to go back / return (to where you belong / where you started / home base)”

Home is considered your base, so when you “go home,” you return there:

家に帰ります。 = “I will go home / return home.”

Using 行きます for “go home” is not natural; the usual verb is 帰る (polite: 帰ります).

Why is there no particle like に or へ after 帰ります? Shouldn’t it be 家に帰ります or something?

The full form could be:

今日は残業がないので、早く家に帰ります。
“Since there’s no overtime today, I’ll go home early.”

In your sentence, the destination is just omitted because it’s obvious from context that “go back” means “go back home.” Japanese often drops information that’s clear from context.

You can say:

早く家に帰ります。
早くうちへ帰ります。

But simply 早く帰ります is very natural, especially in a workplace context where “go back” almost always means “go home.”

How can 帰ります mean “I will go home early”? It looks like present tense, not future.

Japanese basically has two main tense forms:

non-past (like 帰る／帰ります)
past (like 帰った／帰りました)

The non-past form covers both:

present / habitual: “I (usually) go home early.”
future / planned: “I will go home early (today).”

Which one it means depends on context.

In:

今日は残業がないので、早く帰ります。

the presence of 今日は and the reason clause 残業がないので makes it clearly about what will happen (today), so we understand it as “I’ll go home early (today).”

Why isn’t there an explicit “I” in the sentence? How do we know it means “I’ll go home early”?

Japanese often omits subjects (and sometimes objects) when they are clear from context.

Here, the speaker is talking about their own work situation and what they will do because there is no overtime today. In a natural context (e.g., at the office), it’s obvious that the person saying this is talking about their own going home.

If you included the pronoun, it would be:

今日は残業がないので、私は早く帰ります。

That’s grammatically correct, but adding 私は is usually unnecessary and can feel a bit heavy or overly explicit unless you really want to emphasize I (as opposed to someone else).

Can I change the word order, like 残業がないので、今日は早く帰ります? Does that change the meaning?

Yes, you can say:

残業がないので、今日は早く帰ります。

Both:

今日は残業がないので、早く帰ります。
残業がないので、今日は早く帰ります。

are natural. The difference is subtle emphasis:

今日は残業がないので…
- Topic is today: “As for today, since there’s no overtime, I’ll go home early.”
残業がないので、今日は早く帰ります。
- Topic shifts slightly toward today’s action: “…so today, I’ll go home early.”

In everyday conversation, both are fine; the meaning is effectively the same, with only a small nuance difference in what you present as the “topic” first.