fuutou ni juusho o kaitara, yuubinkyoku de kitte o kau.

direct object particle

Breakdown of fuutou ni juusho o kaitara, yuubinkyoku de kitte o kau.

• で: location particle
• 買かう: to buy
• 書かく: to write

Questions & Answers about fuutou ni juusho o kaitara, yuubinkyoku de kitte o kau.

What role does the particle に play in 封筒に?

In 封筒に, に marks the target or location of the action. It tells you where you are writing. So 封筒に住所を書く literally means “to write the address on (the surface of) the envelope.”

Why is 住所 marked with the object particle を?

住所を indicates that 住所 (“address”) is the direct object of 書く (“to write”). In Japanese, you mark what you write with を:
• 文字を書く (“to write characters”)
• 名前を書く (“to write a name”)
• 住所を書く (“to write an address”)

What does the ～たら form in 書いたら express here?

The ～たら conditional (書いたら) can mean “if” or “when/after.” In this sentence it expresses a sequence of actions:

1. 封筒に住所を書いたら – when/after you’ve written the address on the envelope
2. 郵便局で切手を買う – you go buy stamps at the post office

It isn’t hypothetical—rather, it’s saying “once X is done, do Y.”

Why is the location particle で used in 郵便局で?

で marks the place where an action occurs. Here, 郵便局で tells us where you buy the stamps: at the post office. If you omitted で, it’d sound like you’re just listing “post office” without specifying the action location.