Grammar Rule in 30 Seconds
Use 'If' for things that might happen and 'When' for things that definitely will happen in the future.
- Use 'If' for possibilities: 'If it rains, I'll stay home.' (Maybe it rains).
- Use 'When' for certainties: 'When I get home, I'll call you.' (I will definitely get home).
- Never use 'will' immediately after 'if' or 'when' in the condition clause.
Overview
if と when ——は、君の未来の計画を左右する重要なゲートキーパーなんだ。見た目は似てるけど、間違って使うと、上司に対して「このプロジェクトが終わった時に（When）」（自信満々でプロフェッショナル）と言うか、「もしこのプロジェクトが終わったら（If）」（クビにしないでください）と言うか、それくらい大きな違いになっちゃう。英語の文法では、これを First Conditional（第一条件文）と呼ぶよ。これは可能性、予測、そして計画のための言葉なんだ。ゲームでレベルアップする話でも、Netflixのシリーズの結末でも、ピザの配達がいつ来るかでも、どっちを使うべきか知っておく必要があるよ。なんでかって？「彼女に会うもし（If）」と「彼女に会う時（When）」の違いは、「たぶん」と「間違いなく」の違いだからさ。これはリアルタイムで展開する君の人生の文法なんだ。これをマスターすれば、どのWhatsAppグループチャットでも100%自然に聞こえるようになるよ。もしマスターしなかったら...まあ、君がミステリアスなキャラを演じてるってことにしておこうか。なんてね、冗談！君なら絶対できるよ。How This Grammar Works
If は夢見る人、ギャンブラー、そして慎重派のためのもの——起きる確率が50/50のことについて使う。When は計画的な人やリアリストのためのもの——カレンダーに予定が決まっていることについて使うんだ。どちらも基本的なエンジンは同じ。前半は現在形の動詞を使って、後半は未来形（will）を使う。「宇宙との契約」みたいなもんだね。「もし割引してくれるなら、その靴を買うよ（If you give me a discount, I will buy those shoes.）」実用的で、直接的で、正直ちょっとしたパワープレイだよね。もし君の家のネット回線があと5分安定していれば、君はこの文法のエキスパートになれるはず。（今の使い方もわかった？）
Formation Pattern
if または when + Present Simple（現在形）を使った「条件」の節（clause）から始める。注意：未来の話をしているのに、この最初の部分では絶対に will を使わないこと。英語の変なクセだけど、そういうものとして受け入れて。
If（もし） + it rains（雨が降るなら） + , + I（私は） + will stay（滞在するつもり） + home.（家に。）
When（～する時） + I finish（私が終わったら） + , + I（私は） + will call（電話するつもり） + you.（あなたに。）
I + will be + happy（私は幸せだろう） + if（もし） + you come.（あなたが来るなら。）
The food + will arrive（食べ物は届くだろう） + when（～する時） + the driver gets（ドライバーが着く） + here.（ここに。）
Conjugation Table
| Form | Example | Translation |
|---|---|---|
| --- | --- | --- |
| Positive | If I go, I will see. | もし私が行くなら、会うでしょう。 |
| Negative | If I don't go, I won't see. | もし私が行かないなら、会わないでしょう。 |
| Question | Will you go if I go? | もし私が行くなら、あなたは行きますか？ |
| When (Certain) | When it ends, I'll leave. | それが終わったら、私は帰ります。 |
When To Use It
- 「たぶん」のシナリオ（If）: 起きないかもしれないことに使う。「もし懸賞に当たったら、みんなに夕飯をおごるよ（If I win the giveaway, I’ll buy everyone dinner.）」（ネタバレ：たぶん当たらないけど、希望を持つのはいいことだよね）。「プランB」の状況にもピッタリ。「もしフライトがキャンセルされたら、電車で行こう（If the flight is cancelled, we’ll take the train.）」
- 「タイミング」のシナリオ（When）: 避けられないことについて使う。「日が沈んだら、寒くなるだろう（When the sun goes down, it will get cold.）」あるいは、もっと現実的に：「スマホの充電が切れたら、TikTokを見るのをやめるよ（When my phone dies, I will stop scrolling TikTok.）」それが起きるのは分かっていて、その後に何が来るかを話しているだけなんだ。
- 現代の生活: この文法はどこにでもある。「もしこの投稿が気に入ったら、パート2をやるよ（If you like this post, I'll do a part 2.）」「給料が入ったら、あのAirPodsを買うんだ（When I get my paycheck, I’m buying those AirPods.）」「Wi-Fiが遅かったら、データ通信を使うよ（If the Wi-Fi is slow, I'll use my data.）」これは交渉と期待の言語なんだ。あと、後で会う約束について友達に空約束をするのにも最適。「もしあまり疲れてなかったら、行くよ！（If I'm not too tired, I'll come!）」（本当はNetflixを見るために家にいるつもりなのはバレバレだけどね）。
Common Mistakes
Willの使いすぎ: 最大の間違いは、if節の中にwillを入れちゃうこと。 *✗ If I will see him...* ✓ If I see him... 覚えておいて：ifの部分は引き金（トリガー）であって、トリガーは現在にとどまるんだ。- 確実性の取り違え: 全然確実じゃないことに
whenを使うこと。「道で100万ドル拾った時は...（When I find a million dollars on the street...）」落ち着いて、ジェフ・ベゾス。すごく具体的な地図でも持ってない限り、ここはifを使おう。 - コンマのドラマ: 文が
ifやwhenで始まる時にコンマを忘れること。読者が必要とする小さな息継ぎみたいなものだよ。If you leave now, you'll make it.vsIf you leave now you'll make it.（ほら、コンマがあった方がずっとスムーズでしょ？） - Present Simple の罠: he/she/it の時の
-sを忘れちゃうこと。If he arrive...違う！ ✓ If he arrives... 未来の話だとしても（まあ、ここでやってるのは現在-未来の融合みたいなもんだけど）、三人称単数は依然として存在するよ。
Contrast With Similar Patterns
- Zero Conditional（事実）: 「氷を熱すると、溶ける（If you heat ice, it melts.）」これは100%真実で、100%いつでもそうなる。科学的事実だね。First Conditional は未来の特定の出来事について話すもの。「もしこの特定の氷を熱したら、いつかは溶けるだろう（If you heat this specific piece of ice, it will melt eventually.）」
- If vs When（メインイベント）:
If= 0% から 99% の確率。When= 100% の確率。「結婚する時は（When I get married）」と言えば、自信があるってこと。「もし結婚したら（If I get married）」と言えば、選択肢を残しておいてる（そしてたぶんTinderのプロフィールもアクティブなまま）ってこと。 - Second Conditional（夢）: 「もし宝くじが当たったら、島を買うのに（If I won the lottery, I would buy an island.）」これはほぼ不可能なことや、完全に想像上の話。First Conditional は「リアル」な可能性について。「もしお金を貯めたら、新しいノートPCを買うよ（If I save my money, I will buy a new laptop.）」これはただの空想じゃなくて、計画だね。
Quick FAQ
will の代わりに going to は使える？
使えるよ！「彼女に会ったら、話すつもりだ（If I see her, I am going to tell her.）」こっちの方が、もう少し計画済みって感じがするね。
unless はどう？
Unless は単に if not のこと。「雨が降らない限り（Unless it rains）」=「もし雨が降らなければ（If it doesn't rain.）」音節を1つ節約できるね！
can や may は使える？
全然OK。「終わったら、帰っていいよ（If you finish, you can leave.）」これだと結果が「予測」から「許可」に変わるね。
順番は関係ある？
関係ないよ。「遅れるなら電話するよ（I'll call you if I'm late）」は「もし遅れるなら、電話するよ（If I'm late, I'll call you）」と同じ。コンマのルールだけ忘れずに！
なんで if の後に will が来ないの？
英語の先生が訂正したがるポイントの一つなんだよね。if は一瞬だけ君を現在に閉じ込めるタイムマシンだと思って。
誕生日について話す時に when を使っていい？
もちろん。「私の誕生日が来たら、パーティーをするよ（When it's my birthday, I'll throw a party.）」年齢をスキップする予定でもない限り、誕生日は確実に来るからね！
First Conditional Structure
| Clause Type | Conjunction | Subject | Verb Form | Example |
|---|---|---|---|---|
|
Condition
|
If / When
|
I / You / We / They
|
Present Simple (Base)
|
If they arrive...
|
|
Condition
|
If / When
|
He / She / It
|
Present Simple (+s/es)
|
When she arrives...
|
|
Result
|
(None)
|
Any Subject
|
Will + Base Verb
|
...we will start.
|
|
Negative Condition
|
If
|
Any Subject
|
Don't / Doesn't + Base
|
If it doesn't rain...
|
|
Negative Result
|
(None)
|
Any Subject
|
Won't + Base Verb
|
...we won't go.
|
Common Contractions
| Full Form | Contraction | Usage |
|---|---|---|
|
I will
|
I'll
|
Very common in speech
|
|
You will
|
You'll
|
Very common in speech
|
|
He will / She will
|
He'll / She'll
|
Very common in speech
|
|
It will
|
It'll
|
Common, but harder to hear
|
|
Will not
|
Won't
|
Standard negative
|
Meanings
The first conditional describes a real possibility in the future. 'If' introduces a condition that may or may not happen, while 'When' introduces an event the speaker is certain will occur.
Probability (If)
Used when the outcome depends on an uncertain event.
“If you study hard, you will pass the exam.”
“If we leave now, we'll catch the train.”
Certainty/Timing (When)
Used when the event is guaranteed to happen, and we are just waiting for the time to arrive.
“When the sun goes down, it will get cold.”
“When I turn 21, I'll have a big party.”
Immediate Sequence (As soon as)
A stronger version of 'when' emphasizing that the result happens immediately after the condition.
“As soon as the plane lands, I'll text you.”
“I'll pay the bill as soon as I get my salary.”
Reference Table
| キーワード | 可能性 | 意味 | 条件節の例 | 主節の例 |
|---|---|---|---|---|
|
If
|
可能性あり (五分五分)
|
条件が起こるかもしれない
|
If it rains tomorrow,
|
I'll stay home.
|
|
When
|
確実 (100%)
|
イベントは必ず起こる
|
When I get home,
|
I'll eat dinner.
|
|
If
|
低い可能性
|
条件付きの結果
|
If she wins the lottery,
|
she'll quit her job.
|
|
When
|
予想されるタイミング
|
その時点での行動
|
When the clock strikes five,
|
the meeting will end.
|
|
If
|
警告／アドバイス
|
条件の結果
|
If you don't study,
|
you won't pass.
|
|
When
|
予測可能な出来事
|
確実性の結果
|
When the baby cries,
|
I'll feed her.
|
|
Unless
|
否定条件
|
〜でない限り…
|
Unless you hurry,
|
you'll be late.
|
フォーマル度スペクトル
Upon your arrival, would you be so kind as to contact me? (Communication)
When you arrive, please give me a call. (Communication)
Call me when you get there. (Communication)
Hit me up when you're there. (Communication)
ファーストコンディショナル: IfとWhen
If (可能性)
- 条件 (起こるかもしれない／起こらないかもしれない) If + Present Simple
- 結果 (起こりうる結果) will + Base Verb
When (確実性)
- 出来事 (確実に起こる) When + Present Simple
- 結果 (その時点での行動) will + Base Verb
よくある間違い
- If/Whenの後に'will'は使わない e.g., *If it rains*, not *If it will rain*
ファーストコンディショナルでのIfとWhenの比較
IfまたはWhenの選択フローチャート
未来の出来事について話していますか？
その未来の出来事は*確実に*起こりますか？
その未来の出来事は*可能性*があるが確実ではないですか？
「If」と「When」の使い分け
「If」を使うのは…
- • 可能性
- • 条件
- • 不測の事態への計画
- • 警告／アドバイス
「When」を使うのは…
- • 確実な出来事
- • 予想されるタイミング
- • スケジュールされた行動
- • 一連の出来事
注意点…
- • If/Whenの後に'will'は使わない
- • 節が文頭に来る場合はカンマ
- • 意味の明確さ
レベル別の例文
If it is cold, I will wear a coat.
If it is cold, I will wear a coat.
When I go home, I will sleep.
When I go home, I will sleep.
If you are hungry, we will eat.
If you are hungry, we will eat.
When the bus comes, we will get on.
When the bus comes, we will get on.
If I have time, I'll call you later.
If I have time, I'll call you later.
When the movie starts, please be quiet.
When the movie starts, please be quiet.
If she doesn't arrive soon, we'll leave.
If she doesn't arrive soon, we'll leave.
I'll buy a new phone when I have enough money.
I'll buy a new phone when I have enough money.
If the weather stays like this, the crops will fail.
If the weather stays like this, the crops will fail.
When you finish the report, will you send it to me?
When you finish the report, will you send it to me?
If we don't reduce costs, we won't make a profit.
If we don't reduce costs, we won't make a profit.
As soon as I hear any news, I'll let you know.
As soon as I hear any news, I'll let you know.
If the interest rates rise, the housing market will likely cool down.
If the interest rates rise, the housing market will likely cool down.
When the results are published, we'll be able to see the impact.
When the results are published, we'll be able to see the impact.
If you happen to see Mark, will you tell him I'm looking for him?
If you happen to see Mark, will you tell him I'm looking for him?
Unless they provide more funding, the project will be cancelled.
Unless they provide more funding, the project will be cancelled.
Should the negotiations fail, the company will face bankruptcy.
Should the negotiations fail, the company will face bankruptcy.
If you will just sign here, we'll finalize the paperwork.
If you will just sign here, we'll finalize the paperwork.
When the dust finally settles, we'll see who was right.
When the dust finally settles, we'll see who was right.
If it weren't for the rain, we'd be having a great time (Mixed/First overlap).
If it weren't for the rain, we'd be having a great time.
If the minister is to resign, it will happen before the weekend.
If the minister is to resign, it will happen before the weekend.
Whensoever the opportunity arises, I shall take it.
Whensoever the opportunity arises, I shall take it.
If you would be so kind as to wait, the doctor will be with you shortly.
If you would be so kind as to wait, the doctor will be with you shortly.
Provided that the conditions are met, the merger will proceed as planned.
Provided that the conditions are met, the merger will proceed as planned.
間違えやすい
Both use 'if' and present tense. Learners don't know when to use 'will'.
Learners use the First Conditional for impossible things.
Learners want to use 'will' after any time word.
よくある間違い
If it will rain, I stay.
If it rains, I'll stay.
When I will see him...
When I see him...
If he go, I will go.
If he goes, I will go.
I will call you if I will arrive.
I will call you when I arrive.
If I see him I will tell him.
If I see him, I will tell him.
If it rains, I stay home.
If it rains, I will stay home.
When I'll finish, I'll call.
When I finish, I'll call.
If I would see him, I will tell him.
If I see him, I will tell him.
Unless it doesn't rain, we'll go.
Unless it rains, we'll go.
When I win the lottery, I'll buy a car.
If I win the lottery, I'll buy a car.
文型パターン
If I ___, I will ___.
When I ___, I'll ___.
I won't ___ unless ___.
As soon as ___, we will ___.
Real World Usage
If you're free later, let's grab a coffee.
If I am selected for this role, I will work hard to exceed expectations.
When the gate opens, we'll board the plane.
If you spend over $50, you'll get free shipping.
When the water boils, add the pasta.
If the storm continues, flights will be delayed.
「可能性チェック」を考えよう
Is this event definitely going to happen, or is it just a possibility?
If/Whenの後に「Will」はNG！
If it will rainは間違い！
文頭の節にはカンマを
状況がカギ！
Smart Tips
Bite your tongue! Replace 'will' with the simple present tense immediately.
Ask yourself: 'Is there any chance this won't happen?' If yes, use 'if'.
Swap 'when' for 'as soon as'. It adds a sense of priority to your plans.
Use 'Provided that' instead of 'If' to sound more professional and precise.
発音
Contraction Stress
In the result clause, 'I'll' or 'you'll' are usually unstressed. The stress falls on the main verb.
The 'If' Rise
When the 'if' clause comes first, the voice usually rises at the comma to show the sentence isn't finished.
Conditional Rise-Fall
If you go ↗, I'll go ↘.
Standard conditional statement
暗記しよう
記憶術
If is a 'Maybe', When is a 'Date'. Both use the Present, so don't be late!
視覚的連想
Imagine a fork in the road for 'If' (two possible paths). Imagine a straight train track for 'When' (the train will definitely reach the station, it's just a matter of time).
Rhyme
After 'if' or 'when', the 'will' is a sin; use the simple present to let the meaning in.
Story
A traveler is planning a trip. He says, 'When I arrive in London, I'll see the Big Ben.' (Certainty). Then he says, 'If I have enough money, I'll buy a souvenir.' (Uncertainty). He never says 'will' until he's out of the 'if/when' zone.
Word Web
チャレンジ
Write down 3 things you will definitely do tonight (using 'When') and 3 things you might do if you have time (using 'If').
文化メモ
British speakers often use 'should' in the if-clause to sound more polite or to suggest a lower probability.
Americans are very likely to use 'as soon as' in place of 'when' to emphasize promptness in business contexts.
Using 'When' instead of 'If' in negotiations can be a power move to show you assume the deal will happen.
Conditionals in English evolved from Old English 'gif' (if) and 'hwanne' (when).
会話のきっかけ
What will you do if it rains this weekend?
When you finish your English course, how will you use your skills?
If you win a million dollars tomorrow, what's the first thing you'll buy?
What will happen to the environment if we don't change our habits?
日記のテーマ
よくある間違い
Test Yourself
___ it rains tomorrow, we'll stay inside.
Choose the correct sentence:
Find and fix the mistake:
When my boss will call, I'll tell her about the new client.
Translate into English: 'Si me envías un mensaje, te responderé.'
Answer starts with: ["I...
Score: /4
練習問題
8 exercises___ I see him tomorrow, I'll give him your message. (It's possible I will see him, but not certain).
If she ___ (not/study), she will fail the exam.
Find and fix the mistake:
When I will get home, I will make dinner.
If it doesn't rain, we will have a picnic.
A: Are you coming to the party? B: I'm not sure. I'll come ___ I finish my work early.
Select the First Conditional sentence.
1. If you eat too much... 2. When the sun sets... 3. Unless you hurry...
You can use 'will' in both the 'if' clause and the 'result' clause.
Score: /8
Practice Bank
12 exercisesI'll make some coffee ___ you wake up.
If you will study, you will pass the exam.
Choose the correct sentence:
Translate into English: 'Cuando termine el trabajo, te llamaré.'
Arrange these words into a sentence:
Match the situations with the correct word:
Don't worry, I'll text you ___ I'm on my way.
If I will go to London, I'll visit the British Museum.
Choose the correct sentence:
Translate into English: 'Si hace sol, iremos de picnic.'
Arrange these words into a sentence:
Match the event type with the correct word:
Score: /12
よくある質問 (8)
Yes! You can use other modal verbs in the result clause to change the meaning. `If it's sunny, we can go to the beach` (ability/permission) or `If it's sunny, we might go` (lower certainty).
In 99% of cases at B1 level, yes. However, in very formal English, 'will' can be used after 'if' to mean 'if you are willing to' (e.g., `If you will just wait here...`).
`When` is general timing. `As soon as` is immediate. `When I get home, I'll eat` vs. `As soon as I get home, I'll eat` (the second one implies you are very hungry!).
Only if the `if` or `when` clause comes first. If it's in the middle, no comma is needed. `If it rains, I'll stay.` vs `I'll stay if it rains.`
No. The First Conditional is strictly for future possibilities. For the past, you would use the Third Conditional.
That is the Zero Conditional. It means 'Every time I see him, I tell him' (a habit). The First Conditional `I'll tell him` refers to one specific time in the future.
It is neutral. It's used in both conversation and writing. It's often easier than saying 'if... not'.
If the condition is impossible or very unlikely (like winning the lottery for most people), we often switch to the Second Conditional (`If I won...`). But if you just bought a ticket, the First Conditional is fine!
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
Si + Presente / Cuando + Subjuntivo
English uses Present Simple for both 'if' and 'when', while Spanish changes the mood for 'when'.
Si + Présent / Quand + Futur
French uses the future tense after 'when', English does not.
Wenn + Präsens
German uses one word (wenn) for both possibilities and certainties.
〜たら (~tara) / 〜とき (~toki)
Japanese relies on conditional particles rather than a 'will' vs 'present' tense split.
إذا (Idha) / عندما (Indama)
Arabic often uses the past tense form to express the condition clause.
如果 (Rúguǒ) / 当...的时候 (Dāng... de shíhòu)
Chinese uses particles and word order instead of tense changes.
Learning Path
Prerequisites
Learn These First
関連動画
Related Grammar Rules
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