Grammar Rule in 30 Seconds
Use 'when' to link a specific time, day, or era to a description without using clunky prepositions.
- Place 'when' immediately after a time noun like 'day', 'year', or 'moment'. Example: 'The year when we met.'
- The clause following 'when' must contain a subject and a verb. Example: '...when the sun sets.'
- In informal English, 'when' can often be replaced by 'that' or omitted entirely. Example: 'The day (that) we left.'
Overview
when だよ。これは文におけるデジタルのタイムスタンプみたいなものなんだ。スピーチが不格好な説明書みたいにならないように、具体的な瞬間、日、あるいは時代を説明文とつなげるのに役立つんだ。お気に入りのアプリにある「リンク」ボタンだと思えばいいよ。「その日を覚えてる。その時会ったよね（I remember that day. We met then）」って言う代わりに、「私たちが会った日を覚えてるよ（I remember the day when we met）」ってスムーズに言えるんだ。その方が自然だし、流れもいいし、プロっぽく聞こえるでしょ。when を正しく使うのは、英語を「理解できる」レベルから「流暢」なレベルに引き上げる小さな変化の一つなんだ。それは、ぼやけた写真と4K動画くらいの差があるよ。もし聞き手に、君が描写している正確な瞬間をイメージしてほしいなら、when は最高の相棒さ。ただ、鍵をなくした場所を説明するのには使わないでね――それはまた別のルールだから！How This Grammar Works
when を関係副詞と呼ぶんだ。でも、難しい名前にビビらないで。その役割は実はすごくシンプルで、時間を表す名詞を説明する節を導くだけなんだ。「時の単語」（名詞）があって、それについての情報を付け足したいとするでしょ。わざわざ新しい文を始めるんじゃなくて、when を使ってその隙間を埋めるんだ。例えば、「その瞬間（the moment）」について話してて、それが3年前に元カレの写真にうっかり「いいね」しちゃった瞬間だとしたら、when がその2つの考えを完璧につないでくれる。実質的に、on which や at which みたいな前置詞句の代わりになるんだ。「私たちが旅行した日（the day on which we traveled）」と言うのは文法的には正しいけど、まるで19世紀の小説を書いてるみたいに聞こえちゃうよ。現代のテキストメッセージやゲーム、Vlogなら、when 一択だね。簡潔でわかりやすいし、勢いも保てるから。それはポインターみたいな役割をしてて、聞き手に「ねえ、次の言葉でこの特定の時間がなんで特別なのか説明するよ」って伝えるんだ。言語版の「Save the Date（予定空けておいて）」カードみたいなもんだね。
Formation Pattern
day、year、time、moment、era、week、あるいは summer とかでもOK。
when を足す。これがコネクターになるよ。
when を省略することも多いけど、B1学習者は入れておいた方が無難だね。
when + [Subject] + [Verb]。
The summer + when + I + started vlogging was amazing. （私がVlogを始めた夏は最高だった。）
when が in や at みたいな前置詞の代わりになってることに注目して。「The summer when I started vlogging in」とは言わないよね。when の中にもう「時」の意味が含まれてるから。スペースの節約になるね！
When To Use It
when を見かけるはずだよ。YouTubeの「Storytime」動画とか、友達にゲームのバグを説明する時にピッタリだね。期間や時点を特定したい時はいつでも使っていいよ。- Social Media Captions: 「アイスコーヒーとミーム（ネタ画像）だけで生きてた週の 回顧 み（Throwback to the week
whenwe lived on iced coffee and memes）。」 - Work & Zoom Calls: 「プレゼン中にWi-Fiが落ちた時のこと覚えてる？（Do you remember the time
whenthe Wi-Fi cut out during the presentation?）」 - Travel & Vlogging: 「これが私たちが頂上に着いた正確な瞬間です。（This was the exact moment
whenwe reached the summit.）」 - Nostalgia & Daily Life: 「ショッピングモールで何時間もただたむろできた日々が恋しいよ。（I miss the days
whenwe could just hang out at the mall for hours.）」 - Setting Boundaries: 「料理を注文するから、空いてる時間を教えて。（Tell me the time
whenyou’ll be free so I can order the food.）」
when を使えば自分の実績を特定の年や役割とリンクさせられる。君の人生のタイムラインをつなぎ止める接着剤みたいなものさ。これがないと、話がただの日付と事実の羅列になっちゃって、利用規約のページを読むくらい退屈なものになるよ。
Common Mistakes
when の代わりに which や that を使っちゃうこと。- The Preposition Trap: 学習者はよく「The day
whichI met her」って言っちゃう。（間違い！）これにはwhenかon whichが必要なんだ。もしwhichを使うなら、「The dayon whichI met her」みたいに前置詞が必要だよ。でもwhenの方がずっと自然だね。 - Double Time: 「The time
whenit happenedthen」と言わないようにね。節の最後にthenは要らないよ。だってwhenがもうその仕事をしてるから。サングラスを2つかけてるみたいで、重複してるしちょっと変でしょ。 - Confusing with 'Where': 名詞が本当に「時間」かどうか確認して。たまに「The place
whenI was born」って言う人がいるけど、巨大な時計の中で生まれたんじゃない限り、たぶん「The placewhereI was born」って言いたかったんだよね。 - Forgetting the Noun: こういう関係節では、
Whenが指し示す「時の名詞」が必要なんだ。「I rememberwhenwe met」と言うと、ちょっと違う構造（名詞節）になるよ。関係節にするなら、名詞が必要：「I remember thetimewhenwe met」。
Contrast With Similar Patterns
when、which、that のどれを使えばいいか、どうやって判断する？ グループチャットで適切な絵文字を選ぶみたいなもんで、文脈がすべてだよ。whenvs.on which/in which: 意味は同じだけど、whenはカジュアルでイケてる従兄弟って感じ。on whichはフォーマルなメールや学術論文用。それ以外は全部whenでOK。whenvs.that: 多くの場合、whenをthatに置き換えたり、完全に消しちゃっても大丈夫。「The yearwhenI graduated」と「The yearthatI graduated」はどっちもアリ。ただ、whenの方が時間に特化してるから、より明確に聞こえることが多いね。whenvs.where: これが一番簡単。カレンダーや時計の話ならwhen。地図の話ならwhere。- Relative Clauses vs. Question Words: 「The time
whenwe met」のwhenと、「Whenare we meeting?（いつ会う？）」のwhenを混同しないでね。片方はコネクター（関係副詞）で、もう片方は疑問詞だから。
when は専用のツールだと思って。スマホの画面を直すのにハンマーは使わないでしょ？ それと同じで、滑らかに話したいなら、土曜日の午後を説明するのに which は使うべきじゃないよ。Quick FAQ
「ショーが始まる時間（the hour when the show starts）」みたいに、特定の時間にも when は使える？
もちろん！ when はミリ秒から千年紀（ミレニアム）まで、どんな時間の単位にも使えるよ。
when を省略してもいいの？
うん、カジュアルな英語では、「The time when we met」の代わりに「The time we met」って言うことがよくあるよ。テキストメッセージではすごく一般的だね。
when は過去、現在、未来でも使える？
使えるよ！ 「生まれた日（The day when I was born）」（過去）、「幸せを感じる瞬間（The moments when I feel happy）」（現在）、「旅行に行く年（The year when I will travel）」（未来）、全部OK。
when は that よりフォーマルなの？
必ずしもそうじゃないけど、より正確ではあるね。聞き手に「時間の説明が来るぞ」って合図を送れるから。
'every day' の後に when は使える？
使えるよ！ 「太陽が出ている日が大好き（I love the days when the sun is out）」はすごくいい文だね。
もしそれが「時の名詞」かどうかわからなかったら？
その名詞について「何時？」とか「どの日？」って聞けるなら、それは時の名詞だよ。
'the time when' と 'the time at which'、どっち？
どっちも正しいけど、日常会話では 'the time when' の方が圧倒的に一般的だね。「At which」は法的契約書とか、めちゃくちゃ豪華な結婚式の招待状を書いてるみたいに聞こえるよ。
就職面接で when を使ってもいい？
間違いなく。経験した期間を明確に定義するのに役立つよ。例えば「Googleで働いていた2年間（The two years when I worked at Google）」みたいにね。
Sentence Structure with 'When'
| Time Noun (Antecedent) | Relative Adverb | Subject | Verb Phrase | Function |
|---|---|---|---|---|
|
The day
|
when
|
we
|
met
|
Defining the specific day
|
|
The year
|
when
|
I
|
was born
|
Identifying a specific year
|
|
A time
|
when
|
life
|
was simpler
|
Describing a general period
|
|
The moment
|
when
|
she
|
laughed
|
Capturing a precise point
|
|
The decade
|
when
|
it
|
happened
|
Contextualizing an era
|
Meanings
A relative adverb used to introduce a clause that provides more information about a noun denoting a period of time.
Defining Time
Identifying exactly which time or period is being discussed.
“Sunday is the day when I usually do my laundry.”
“The 1960s was a decade when many social changes occurred.”
Non-Defining Time
Adding extra, non-essential information about a time that is already identified.
“In 2020, when the pandemic started, the world changed.”
“Last Christmas, when we were in London, it actually snowed.”
Formal Substitution
Replacing 'in/on/at which' to make sentences sound more natural.
“The moment when (at which) she realized the truth was dramatic.”
“The era when (in which) dinosaurs lived lasted millions of years.”
Reference Table
| 時を表す名詞 | 関係副詞 | 行動・出来事 | 例文 |
|---|---|---|---|
|
The day
|
when
|
we met
|
I remember the day when we met.
|
|
The year
|
when
|
I was born
|
What was the year when you were born?
|
|
A time
|
when
|
I need advice
|
She's the person to call at a time when I need advice.
|
|
The moment
|
when
|
he smiled
|
That was the moment when he smiled.
|
|
My childhood
|
when
|
I lived in London
|
My childhood when I lived in London was unforgettable.
|
|
The period
|
when
|
she studied abroad
|
The period when she studied abroad changed her life.
|
|
An occasion
|
when
|
they celebrate
|
Christmas is an occasion when families gather.
|
フォーマル度スペクトル
I recall the specific occasion when we first convened. (Memory)
I remember the time when we first met. (Memory)
I remember when we first met. (Memory)
Remember that time we first linked up? (Memory)
レベル別の例文
I like the time when we eat pizza.
Monday is the day when I go to school.
I remember the moment when you said hello.
Is this the time when the bus comes?
Winter is the season when it snows a lot.
There was a year when we lived in Spain.
I don't like days when it is very cold.
Do you know the hour when the shop opens?
I'll never forget the day when I got my first job.
Can you suggest a time when we can meet tomorrow?
The 1990s was a decade when technology changed fast.
He arrived at a moment when everyone was leaving.
In 2010, when the economy was struggling, many people lost their homes.
There are times when I feel like quitting, but I keep going.
The era when coal was the main fuel is coming to an end.
I need to find a day when both of us are free for a long talk.
The precise juncture when the two companies merged remains a point of debate.
We are living in an age when privacy is becoming a luxury.
Rarely is there a moment when the city is truly silent.
The period when the artist lived in Paris was his most productive.
The zeitgeist of the era, when existentialism reigned supreme, is reflected in his work.
One can scarcely imagine a time when such behavior would have been tolerated.
The very second when the catalyst is added, the reaction begins.
It was a dark epoch when superstition often overrode scientific inquiry.
間違えやすい
Learners use 'which' for time because they think of the day as a thing.
In informal English, 'that' can replace 'when', which confuses learners about the 'real' rule.
'Whenever' means 'any time', while 'when' refers to a specific time.
よくある間違い
The day which I saw you.
The day when I saw you.
I remember when the time.
I remember the time when...
The day when I met you on.
The day when I met you.
When is the day you come?
What is the day when you come?
The summer when it was hot in.
The summer when it was hot.
Sunday is the day when I am going.
Sunday is the day when I go.
The year when I was born it.
The year when I was born.
The time when I spent in Paris.
The time which I spent in Paris.
In 2010 when I was a student I lived in London.
In 2010, when I was a student, I lived in London.
The moment when that I realized...
The moment when I realized...
The era when in which we live.
The era in which we live.
文型パターン
I'll never forget the day when ___.
___ is the time of year when ___.
There are moments when ___.
Can you think of a time when ___?
Real World Usage
Tell me about a time when you handled a conflict.
That moment when the coffee finally kicks in.
Is there a day when the museum is free?
It was a century when empires fell.
Remember the night when we got lost?
The hour when the polls close is 8 PM.
「when」で時をピンポイントに！
「when」と「where」を混同しないで！
カジュアルな会話では「when」を省略することも
字幕で「when」の使い方をチェック！
自分の思い出で練習してみよう！
Smart Tips
Try replacing 'when' with 'in which' or 'during which' to sound more academic.
Delete the preposition immediately. 'When' does all the work by itself.
Use 'The moment when' to create a sense of drama and focus.
Try to put 'it' at the end of the clause. If it works, use 'which'. If you need 'on it', use 'when'.
発音
Weak Form of 'When'
In rapid speech, 'when' is often unstressed and sounds like /wən/.
Linking
The 'n' in 'when' often links to the following vowel. 'When I' sounds like 'whe-ni'.
Relative Clause Dip
The day ↘ when we met ↗ was sunny.
The pitch usually drops slightly during the relative clause to show it is parenthetical information.
暗記しよう
記憶術
When for the 'When' (time), Where for the 'Where' (place).
視覚的連想
Imagine a clock face that has a bridge growing out of it. The bridge connects the clock to a movie screen showing an action. The bridge is labeled 'WHEN'.
Rhyme
If it's a day, a year, or a time, use 'when' to make your sentence climb!
Story
Once there was a lonely 'Monday'. It wanted to tell everyone it was special. It met a connector named 'When'. Together, they became 'The Monday when I won the lottery', and everyone finally understood why it was special.
Word Web
チャレンジ
Write three sentences about your favorite childhood memories using 'The year when...', 'The day when...', and 'The time when...'.
文化メモ
Using 'the time when' is a very common way to start a story or anecdote in English-speaking cultures.
In formal papers, writers often prefer 'the period in which' over 'the time when' to sound more objective.
In both US and UK casual speech, 'when' is frequently dropped if the noun is 'time' or 'day'.
From Old English 'hwanne', which was originally an interrogative adverb.
会話のきっかけ
Can you tell me about a time when you felt really proud of yourself?
What is the best time of year when someone should visit your country?
Do you remember the day when you first started learning English?
Is there a specific hour of the day when you feel most productive?
日記のテーマ
よくある間違い
Test Yourself
My favorite season is autumn, ___ the leaves change color.
Find and fix the mistake:
The concert which starts at 8 PM is going to be amazing.
Arrange the words in the correct order:
All words placed
Click words above to build the sentence
Score: /3
練習問題
8 exercisesI'll never forget the day ___ we first met.
The year ___ I spent in Italy was the best of my life.
Find and fix the mistake:
That was the summer when we went to France in.
remember / the / do / you / when / time / we / lost / got / ?
1. The morning... 2. The year... 3. The moment...
You can use 'when' to replace 'on which'.
A: Why do you love autumn? B: It's the season ___ the leaves change color.
I know the day when he arrives.
Score: /8
Practice Bank
12 exercisesI'll never forget the year ___ I graduated from college.
Choose the correct sentence:
Can you tell me the moment where you knew it was over?
Translate into English: 'I love the time when the city is quiet.'
Arrange these words into a sentence:
Match each time expression with its correct 'when' clause:
This is the restaurant ___ we celebrated my birthday last year.
Tell me a story about a time where you were really brave.
Which sentence is correct?
Translate into English: 'I cherish the days when we had no responsibilities.'
Arrange these words into a sentence:
Match the start of the sentence with its correct ending:
Score: /12
よくある質問 (8)
Yes, in informal English, `that` is very common, especially after 'day' or 'time'. Example: 'The day `that` we met.'
Yes, if the time noun is the object of the main clause. 'I remember the day (when) we met.' This is very common in spoken English.
`In which` is much more formal. You would use it in an academic essay, whereas `when` is used in daily conversation.
Absolutely. You can say 'The very second `when` the bomb exploded.' It works for any duration of time.
Because `when` already acts as the prepositional phrase 'on which'. Adding 'on' again is like saying the same thing twice.
As a relative adverb, yes. If there is no noun, it is likely a subordinating conjunction or a question word.
No, `where` is strictly for locations. However, some languages (like French) use the same word for both, which causes confusion.
It is not redundant; it is grammatically standard. While you can say 'I remember when...', adding 'the time' makes it a relative clause.
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
cuando / en que
Spanish speakers often forget that 'when' doesn't need a preposition in English.
où / quand
French speakers often say 'the moment where' instead of 'the moment when'.
als / wenn
English uses 'when' for both single past events and general times.
時 (toki)
The word order is reversed, and there is no 'when' equivalent acting as a bridge.
عندما (indama) / حين (hina)
English forbids the resumptive pronoun (e.g., 'the day when I saw him *in it*').
的时候 (de shihou)
Chinese speakers often struggle with the 'Noun + when' order in English.
Learning Path
Prerequisites
Learn These First
関連動画
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