kinou ha tizu wo wasuremasita.

I forgot the map yesterday.

Breakdown of kinou ha tizu wo wasuremasita.

• は: topic particle
• を: direct object particle
• 昨日きのう: yesterday
• 地図ちず: map
• 忘わすれる: to forget

Questions & Answers about kinou ha tizu wo wasuremasita.

Why is は used after 昨日?

In this sentence, は marks 昨日 (“yesterday”) as the topic of the statement—“As for yesterday, (I) forgot the map.” It tells the listener that you’re setting 昨日 as the frame of reference. Without は, 昨日 would simply act as a time adverbial (“yesterday I…”), but adding は makes it explicitly topical and can lend a slight emphasis or contrast (“Yesterday, at least, I forgot it”).

Why is を used after 地図?

The particle を marks 地図 (“map”) as the direct object of the verb 忘れる (“to forget”). In Japanese, when a verb acts directly on something, you place を after that thing:

• 地図を忘れました
  = “(I) forgot the map.”

What form of the verb is 忘れました, and how does it relate to 忘れる?

忘れました is the polite past form of the verb 忘れる.

• Root (dictionary) form: 忘れる
• Polite non-past: 忘れます (“forget/ will forget”)
• Polite past: 忘れました (“forgot”)
  You use the polite form in most everyday conversations with people you’re not extremely close to, or in formal situations.

Why is there no explicit subject like “I” in the sentence?

In Japanese it’s very common to omit the subject when it’s clear from context. Here, because you’re talking about forgetting a map, the listener can infer that I (the speaker) is the one who forgot it. If you really need to specify, you could say 私は at the start, but it’s usually unnecessary.

Why does the verb come at the end of the sentence?

Japanese follows a Subject–Object–Verb (SOV) word order. That means the verb typically comes last. So you list the time/topic (昨日は), then the object (地図を), and finally the verb (忘れました).

Can I omit は after 昨日 and just say 昨日地図を忘れました? What changes?

Yes, you can say 昨日地図を忘れました. In that case 昨日 simply functions as a time adverb without the topical nuance. The sentence still means “I forgot the map yesterday,” but it feels slightly more neutral or straightforward. Adding は adds a subtle “as for yesterday…” emphasis.

How would I specify “my map” instead of just “the map”?

You can add a possessive 私の before 地図:

• 昨日は私の地図を忘れました。
  This makes it clear you’re talking about your own map. In many contexts though, just 地図 is enough if it’s obvious whose map it is.

How can I make this sentence more casual (e.g. with friends)?

You can switch from the polite ました ending to a plain past ending 忘れた and drop particles if you like:

• 昨日地図忘れた。
  This is common in very casual speech or text messages. If you still want は, you could say 昨日は地図忘れた.