Learn Hardcore Japanese: eki de eiga no posutaa wo mimasita.

In this sentence, で marks the location where the action took place. It answers “where” you performed the verb 見ました (“saw”). So 駅で means “at the station.”

Why don’t we use は instead of で with 駅?

The particle は marks the topic of the sentence, not the location of an action. If you said 駅は映画のポスターを見ました, you’d be saying “As for the station, it saw the movie poster,” which doesn’t make sense. To indicate “at the station” as the place where you saw something, you need で.

What is the role of の in 映画のポスター?

The particle の connects two nouns in a possessive or descriptive way. Here 映画のポスター literally means “poster of a movie” or “movie poster.” 映画 modifies ポスター.

Why do we use を with ポスター in ポスターを見ました?

The particle を marks the direct object of a transitive verb. Since ポスター is what you saw, it takes を before the verb 見ました.

Why is the verb 見ました in the past tense?

見ました is the polite past form of 見る (“to see”). It indicates the action was completed in the past. If you’re telling someone that you have already seen the poster, you use the past tense.

What’s the difference between 見ました and 見た?

Both are past tense of 見る, but 見ました is polite (ます-form), while 見た is plain/casual. You’d use 見た with friends or in writing like diaries: 駅で映画のポスターを見た.

Why is the word order 駅で映画のポスターを見ました instead of 映画のポスターを駅で見ました?

Japanese has flexible word order, but the typical pattern is Subject–(Adverbials)–Object–Verb. Location phrases like 駅で usually come before the object. Both orders are grammatically correct, but placing 駅で first sounds more natural and emphasizes the place.

Could we omit 映画の and say 駅でポスターを見ました? Would that still work?

Yes, 駅でポスターを見ました is grammatically fine, but more vague. It means “I saw a poster at the station” without specifying it’s a movie poster. Use 映画のポスター whenever you want to clarify what kind of poster.

Why is there no explicit subject? Who is doing the action?

Japanese often omits subjects when they’re obvious. Here, it’s understood that I (the speaker) saw the poster. If you need to be explicit, you can add 私は at the beginning: 私は駅で映画のポスターを見ました (“I saw a movie poster at the station”).