Learn Hardcore Japanese: yasumi ga ookereba, kaigairyokou ni ikeru. - If there are many days off, I can go on an overseas trip.

は tends to mark a topic and often contrasts with something else or sets a general theme.
が fits more naturally inside a conditional clause like this, where the focus is on the condition itself.

You could see 休みは多ければ… in some contexts, but it sounds marked/contrasty, like “As for days off, if they are many, then…”, which is less neutral than the usual 休みが多ければ.

Why is 休み used here instead of something like 休みの日 or 休暇?

In everyday conversation, 休み by itself commonly means:

days off (from work/school)
time off / vacation (in a casual sense)

So 休みが多ければ = “If I had a lot of days off / time off”.

Alternatives:

休みの日が多ければ – literally “if there are many days off,” slightly more explicit, but often unnecessarily long.
休暇が多ければ – uses 休暇, a bit more formal and often used for official leave or vacations in a work context.

In colloquial speech, 休み is the most natural and common choice here.

What exactly is 多ければ? How is it formed from 多い?

多ければ is the -ば conditional form of the i-adjective 多い (“many / much”).

For i-adjectives:

Start with the dictionary form: 多い
Drop the final い → 多
Add ければ → 多ければ (“if [something] is many/much”)

Meaning here:
休みが多ければ = “If (the) days off are many” → “If I have a lot of days off”.

Other examples of i-adjective + -ければ:

高い → 高ければ (“if [it] is expensive / high”)
おいしい → おいしければ (“if [it] is delicious”)

Could you also say 休みが多いなら instead of 休みが多ければ? What’s the difference?

Yes, you can say:

休みが多いなら、海外旅行に行ける。

Both mean roughly “If I have a lot of days off, I can go abroad,” but there is a nuance difference:

〜多ければ (-ば form):
- A bit more formal / written-sounding.
- Feels more “logical” or condition-focused.
- Common in explanations, writing, and somewhat careful speech.
〜多いなら (なら form):
- More conversational.
- Often assumes or reacts to some given condition or supposition (“if it’s true that…”).

In many everyday contexts, they are interchangeable, but 多ければ sounds slightly more neutral and structured, while 多いなら feels a bit more like “if it turns out that I have many days off, then…”.

How does this -ば conditional compare with 〜たら or 〜と in this sentence?

Possible variants:

休みが多ければ、海外旅行に行ける。
休みが多かったら、海外旅行に行ける。
休みが多いと、海外旅行に行ける。

Nuances:

〜ば (多ければ):
Logical, somewhat formal/neutral conditional; often used for general conditions or rules.
〜たら (多かったら):
Very common in spoken Japanese; often used for more specific or situational “when/if” situations. Here it feels like “If I ever happen to have many days off, then I can go.”
〜と (多いと):
Often used for habitual, automatic, or cause–effect relationships (“if/when X happens, Y always follows”).
休みが多いと、海外旅行に行ける。 sounds like a general rule: “When/if (I) have many days off, (I) can go abroad [as a general pattern].”

All three are grammatically okay here; -ば is a good, neutral textbook choice.

What does に do in 海外旅行に行ける? Why not へ?

In 海外旅行に行ける, the particle に marks the destination/goal of the movement 行く:

海外旅行に行く = “go on an overseas trip / travel abroad.”

You might have learned:

〜に行く = go to X (place/activity)
〜へ行く = go toward/to X

Here, に is more common because:

海外旅行に行く is a fixed, natural-sounding expression for “go on an overseas trip”.
海外旅行へ行く is not wrong, but sounds a bit more written or slightly stiffer.

In everyday speech, に行く is the default choice for “go to/on X” in this kind of phrase.

What is 行ける exactly, and how is it different from 行く or 行くことができる?

行ける is the potential form of the verb 行く (“to go”).

行く = “to go”
行ける = “can go / be able to go”

So:

海外旅行に行く。 = “(I) go on an overseas trip.”
海外旅行に行ける。 = “(I) can go on an overseas trip.”

行くことができる also means “can go,” but:

行ける is shorter and very common in speech.
行くことができる is more formal, often used in writing or polite announcements.

In most conversation, 行ける is the natural choice.

Where is the word “I” in this sentence? Why isn’t it written?

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

English: “If I had a lot of time off, I could go on an overseas trip.”
Japanese: 休みが多ければ、海外旅行に行ける。
(Literally: “If days off are many, [can] go on an overseas trip.”)

The listener understands from context that the speaker is talking about themself (or maybe “we” or “you”) even though 私 is not explicitly stated.

You could say:

私に休みが多ければ、海外旅行に行ける。 (awkward)
休みが多ければ、海外旅行に行けます。 (polite, still subjectless)

In natural Japanese, explicit “I” (私) is often omitted when unnecessary.

How would I make this sentence more polite?

The easiest way is to change the verb 行ける to its polite form 行けます:

休みが多ければ、海外旅行に行けます。

This is polite but still sounds natural and not overly formal.

You could also make everything more formal with different vocabulary or longer constructions, but usually this is enough for standard polite speech.

Can I say 海外旅行に、休みが多ければ行ける with the parts in a different order?

That word order is grammatically possible but feels unnatural in normal speech.

In Japanese, the most natural order is often:

[Condition clause], [main clause].

So:

休みが多ければ、海外旅行に行ける。 ← natural

If you move 海外旅行に before the comma:

海外旅行に、休みが多ければ行ける。
This sounds somewhat awkward and marked; the listener has to wait longer to understand the condition.

While Japanese word order is more flexible than English, conditional clauses like 〜ば are usually placed first, then the result clause.

Why is there a comma after 多ければ? Is it required?

The comma after 多ければ is:

A reading aid, telling you to pause slightly.
A way to clearly separate the condition from the result.

In Japanese, commas are not always strictly required grammatically, but they are very common in sentences with:

conditionals (〜ば, 〜なら, 〜たら, 〜と)
long or complex clauses

So both of these are acceptable in principle:

休みが多ければ、海外旅行に行ける。 ← standard, recommended
休みが多ければ海外旅行に行ける。 ← possible, but less clear visually

Writing the comma is the usual, clearer style.

Does 休みが多ければ mean “more time off than now” or just “a lot of time off”?

On its own, 休みが多ければ literally means “if the days off are many” → “if there is a lot of time off.”

It does not automatically imply comparison (like “more than now”). Context decides:

If the context is comparing with your current situation, it can be understood as “if I had more days off (than I currently do)”.
If there’s no comparison, it’s just “if I (generally) have a lot of time off.”

If you want to clearly say “more time off (than now)”, a common phrasing is:

もっと休みがあれば、海外旅行に行ける。
(“If I had more time off, I could go on an overseas trip.”)

Here, もっと explicitly gives the “more” comparative nuance.

Could I say 休みが長ければ instead of 休みが多ければ? What’s the difference?

You can say 休みが長ければ, but the nuance changes:

休みが多ければ:
“If I have many days off” → focuses on the number of days off.
休みが長ければ:
“If my vacation is long” → focuses on the length/duration of the break.

For example:

Short but frequent days off → 多い but not 長い.
One long continuous vacation → 長い but not necessarily 多い (only one break).

In the original sentence, 多ければ emphasizes having many days off (or a lot of time off), not necessarily one long continuous vacation.