kinou wa toshokan de benkyoushimasen deshita.

I did not study at the library yesterday.

Breakdown of kinou wa toshokan de benkyoushimasen deshita.

• は: topic particle
• 勉べん強きょうする: to study
• で: location particle
• 昨日きのう: yesterday
• 図書館としょかん: library
• 〜ませんでした: negative polite past form

Questions & Answers about kinou wa toshokan de benkyoushimasen deshita.

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

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

In 昨日は図書館で勉強しませんでした。, nothing explicitly says “I”, but in a normal conversation the default assumption is that the speaker is talking about themselves. So it is understood as:

• (私は) 昨日は図書館で勉強しませんでした。
  → (I) didn’t study at the library yesterday.

You would add a subject when it’s not obvious, or when you want to emphasize it:

• 彼は昨日は図書館で勉強しませんでした。
  He didn’t study at the library yesterday.
• 私は昨日は図書館で勉強しませんでした。
  I didn’t study at the library yesterday. (emphasizing “I” as opposed to someone else)

Why is は after 昨日? I thought は usually comes after the subject like 私は.

は marks the topic, not necessarily the grammatical subject.

In 昨日は図書館で勉強しませんでした。, 昨日 (yesterday) is being set as the topic:

• 昨日は …
  As for yesterday, …

So the sentence is like “As for yesterday, I didn’t study at the library.”

You can also make 私 the topic:

• 私は昨日図書館で勉強しませんでした。
  As for me, I didn’t study at the library yesterday.

Both are correct; they just spotlight different things:

• 昨日は…: talking about what happened (or didn’t happen) yesterday.
• 私は…: talking about what I did (or didn’t do).

Japanese often puts time expressions with は at the start of the sentence to frame the time as the topic:
今日は忙しいです。 – As for today, I’m busy.

Why is it 図書館で and not 図書館に? What’s the difference?

Both で and に can follow places, but they have different roles.

• で marks the location where an action takes place.
• に usually marks destination, goal, or existence.

Here, 勉強する (to study) is an action done at the library, so you use で:

• 図書館で勉強します。
  I study at the library.

Compare:

• 図書館に行きます。 – I’m going to the library. (destination)
• 図書館で本を読みます。 – I read books at the library. (place of action)

Using 図書館に勉強します would be unnatural; 勉強する is not “go to study” but “to study”, so you mark the place of the action with で.

How is 勉強しませんでした formed from 勉強する? Why does it look like “did not do”?

The base verb is 勉強する (to study). To get “did not study” in polite form, you do:

1. Dictionary form: 勉強する
2. Polite non-past (do/will study): 勉強します
3. Polite non-past negative (do not / will not study): 勉強しません
4. Polite past negative (did not study): 勉強しませんでした

So しませんでした is the polite past negative of する.

• 勉強しました = (I) studied.
• 勉強しませんでした = (I) did not study.

Even though you can see ません and でした inside it, as a whole ませんでした is just the past negative polite ending.

Is しません でした two separate words, or one form しませんでした?

Grammatically, it’s one combined verb form: しませんでした (past negative polite).

In writing, you usually don’t insert a space in Japanese anyway, so you’d write:

• 勉強しませんでした。

When Japanese people think about conjugation, they treat しませんでした as a single unit for “did not do” (in polite speech). You may see it broken down in textbooks to show how it’s formed, but in normal use it functions as one verb ending.

What’s the difference between 勉強しませんでした and 勉強しなかった?

They mean the same thing (“did not study”), but differ in politeness and formality.

• 勉強しませんでした。
  – Polite / formal
  – Used with teachers, strangers, in business, etc.

• 勉強しなかった。
  – Plain / casual
  – Used with friends, family, people close to you.

Same meaning, different register.

You can think of it like:

• しませんでした ≈ “did not study”
• しなかった ≈ “didn’t study” (more informal)

Is 勉強 a noun or a verb? Why does it look like a noun plus する?

勉強 by itself is a noun meaning “study” or “studying”.

Japanese has many “noun + する” patterns where adding する (“to do”) turns the noun into a verb:

• 勉強する – to study
• 運動する – to exercise
• 電話する – to telephone
• 練習する – to practice

In your sentence, 勉強しませんでした comes from 勉強する:

• 勉強する – to study
• 勉強しませんでした – did not study

So grammatically it’s “to do study,” but in English we just say “to study.”

Can I say the words in a different order, like 図書館で昨日は勉強しませんでした? What word order is natural?

Japanese word order is flexible as long as the particles are correct, but some orders sound more natural than others.

The most natural and common pattern is:

1. Time
2. Place
3. Verb

So:

• 昨日は図書館で勉強しませんでした。
  (Time) (Topic) (Place) (Verb)
  Yesterday, I didn’t study at the library.

Other possible orders:

• 図書館で昨日は勉強しませんでした。 – Understandable, but sounds odd; the topic 昨日は is usually better near the front.
• 図書館で昨日勉強しませんでした。 – OK, but “yesterday” being non-topic here gives a slightly different feel.

As a learner, it’s safest to stick with:

• [Time] は [Place] で [Verb]。
  → 昨日は図書館で勉強しませんでした。

Can I say 昨日、図書館で勉強しませんでした。 without は? Does that change the meaning?

Yes, you can say:

• 昨日、図書館で勉強しませんでした。

Dropping は makes 昨日 just a normal time expression, not the topic marked for contrast. The nuance difference:

• 昨日は図書館で勉強しませんでした。
  – As for yesterday, I didn’t study at the library.
  – Often has a slight contrast: maybe you did study on other days.

• 昨日、図書館で勉強しませんでした。
  – Simply states what happened yesterday, more neutral.
  – No special contrast implied.

In many everyday contexts, people omit は after adverbs like 昨日, 今日, 明日, unless they want the topic/contrast nuance.

How do I pronounce each part: 昨日, 図書館, 勉強, and the whole sentence?

Here’s a simple pronunciation guide (romaji):

• 昨日 – きのう – ki-noo (long “o” sound)
• は – wa (as the particle, it’s pronounced “wa,” not “ha”)
• 図書館 – としょかん – to-sho-kan
• で – de
• 勉強 – べんきょう – ben-kyoo (long “o” in きょう)
• しませんでした – しませんでした – shi-ma-sen-deshita

Whole sentence:

• 昨日は図書館で勉強しませんでした。
  → Kinō wa toshokan de benkyō shimasen deshita.

Natural speech will flow these together smoothly, but the above breakdown is a good starting point.