watashi wa natsuyasumi ni kaigairyokou no keikaku o kimemasu.

topic particle

Breakdown of watashi wa natsuyasumi ni kaigairyokou no keikaku o kimemasu.

• 私わたし: I
• を: direct object particle
• の: possessive case particle

Questions & Answers about watashi wa natsuyasumi ni kaigairyokou no keikaku o kimemasu.

Why is は used after 私, and what would change if I used が instead?

は marks the topic of the sentence: what you’re talking about.

• 私は夏休みに海外旅行の計画を決めます。
  → As for me, I (will) decide the plan for an overseas trip in summer vacation.

If you used が:

• 私が夏休みに海外旅行の計画を決めます。

This sounds like you’re emphasizing that I (and not someone else) am the one who will decide the plan. It answers an implicit question like “Who will decide it?”

So:

• 私は… = setting up “me” as the general topic.
• 私が… = focusing on “I” as the specific doer, often in contrast to others.

In most neutral contexts, 私は is more natural here than 私が.

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What does に mean in 夏休み + に? Is it “in”, “on”, or “during”?

In 夏休みに, the particle に marks the time when something happens.

It can be translated in several ways depending on context:

• in summer vacation
• during summer vacation
• over the summer break
• for the summer vacation (when you mean “at that time”)

So:

• 夏休みに海外旅行の計画を決めます。
  → I will decide the plan for an overseas trip *during (or in) summer vacation.*

You can think of X に (do something) as “do something at/on/in X (time)”.

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Why is there a の between 海外旅行 and ? What does mean exactly?