Grammar Rule in 30 Seconds
Use modals like 'can' or 'might' in the result clause to show ability, advice, or possibility instead of just certainty.
- Use Present Simple after 'if' (If it rains...)
- Use a modal + base verb in the result (we can stay).
- Never use 'will' in the 'if' part of the sentence.
Overview
will ばっかり使ってたら、自信過剰な占い師みたいに聞こえちゃうよ。現実世界では、可能性とか許可とか、控えめな提案とかがあるわけで。そこで登場するのが、いろんな助動詞を使った First Conditional（仮定法現在）だね。「何が起きるか（will）」だけじゃなくて、「起きるかもしれないこと（might）」、「すべきこと（should）」、「できること（can）」が言えるようになるんだ。「もし鍵が見つかったら、出かける（will leave）」と「もし鍵が見つかったら、やっとパニックにならずにパーティーに行ける（can ... go）」の違いだね。片方は事実で、もう片方は「やっと大惨事を回避できる能力」についての話。might を使おう。偉そうに言いたい？なら must。親切な友達でいたい？なら should だ。これをマスターしないと、上司に「時間があれば、私のレポートを読みます（you will read）」なんて言っちゃうかも（これじゃ脅迫だよ）。本来なら「時間があれば、レポートを読んでいただけますか（you could read）」って言うべきところをね（これならプロっぽい社会人だ）。GPSだってこれを使ってるよ！「この曲がり角を過ぎたら、新しいルートを探す必要があるかもしれません（you may need）」ってね。「あなたは永遠に迷子になります（you will be lost）」なんて言わないあたり、礼儀正しいよね。How This Grammar Works
If + Present Simple（現在形）、will + Base Verb（動詞の原形）。英語学習者にとっては基本中の基本だ。でも will はワンパターンなんだ。「確実性」しか表現できないからね。will を can, may, might, should, must みたいな他の助動詞に入れ替えても、「If」の部分は全く同じ。魔法が起きるのは結果節（帰結節）の方だ。if 節が条件（「トリガー」）を設定する。助動詞がいる結果節は、結果の *種類* を教えてくれるんだ。可能性？義務？それともアドバイス？例えばゲーム中にチームメイトが If we capture the flag, we can win（旗を取れば勝てる）って言ったら、それは勝つ *可能性* や *能力* の話であって、確定した予言じゃない。もし彼らが
we will win って言ったら、たぶん油断して負けるフラグだね。助動詞を使うとニュアンスが出るし、ぶっちゃけ「人生は何が起こるかわからない」とわかってるネイティブっぽく聞こえるよ。
Formation Pattern
if で始める。主語を足す。そして Present Simple を使う。そう、未来の話でも現在形だ。英語って変だよね。「If I will go」とは言わない。ただ If I go と言うんだ。
if 節から始めるなら、コンマが 必須。文をひっくり返せば、コンマはいらない。
can, might, should など）。そして Base Verb（原形、to なしの不定詞）を足す。-s も -ing も -ed もいらない。生の動詞そのままで。
When To Use It
- Possibility (
might,may): 五分五分くらいの時に使う。「If I get my paycheck today, I might buy those new sneakers on Amazon.」（今日給料が入ったら、Amazonであの新しいスニーカーを買うかも。）銀行口座に約束してるわけじゃない。ただの夢想だね。 - Ability or Permission (
can): 社交的な場面に最適。「If you’re free tonight, we can hop on Discord and play some Valorant.」（今夜暇なら、Discordに入ってValorantできるよ。）アプリとかでも：「If you upgrade to Premium, you can skip all the ads.」（プレミアムにアップグレードすれば、広告を全部スキップできます。） - Advice (
should,ought to): 良き友人（あるいはお節介な人）用。「If you want to pass the exam, you should probably stop scrolling TikTok for five hours straight.」（試験に受かりたいなら、TikTokを5時間ぶっ続けで見るのはやめたほうがいいよ。）これは提案であって、法律じゃない。 - Obligation (
must,have to): 「ガチ」モードだね。「If you use the company kitchen, you must clean up your mess.」（会社のキッチンを使うなら、片付けなきゃいけない。）もしやらなかったら、後で怒りのSlackメッセージが来るだろうね。
might」）、ただ出前を頼む時も（「配達員が来たら、やっとご飯が食べられる can」）、こういう助動詞を使えば、人生をありのままに表現できる柔軟性が手に入る。人生ってのは、面倒で、不確かで、選択肢がいっぱいあるもんだからね。
Common Mistakes
If I will see him, I will tell him.って言いたくなるかもしれないけど、そこでストップ！
if 節の中では、現在は未来を含んでるんだ。単に If I see him でいい。脳は未来のことだから will を入れたがるけど、必要のないコーヒーを買いたい衝動と戦うみたいに、その衝動とも戦わなきゃダメだ。can, might, should みたいな助動詞はすごく自立してるんだ。手を繋ぐ to なんていらない。you should go が正解で、you should to go は間違い。唯一の例外は、助動詞ファミリーの変わり者の従兄弟、have to と ought to だけ。あと、三単現の -s にも気をつけて。助動詞は絶対変化しない。he can だよ、he cans じゃない。スープ（can）の話なら別だけど、それはまた別のレッスンで。最後に、確信度を混同しないこと。「そのピザを全部食べたら、気持ち悪くなるかもよ（might）」と言うほうが、「気持ち悪くなる（will）」と断定するよりずっと現実的だ。鉄の胃袋を持ってる人もいるからね。侮っちゃいけない。Contrast With Similar Patterns
標準的な will を使った First Conditional とどう違うの？全部「バイブス（雰囲気）」の問題だね。
will: If I study, I will pass.（勉強すれば、合格する。）これは約束。確信してる。未来の自分はもうお祝いしてる。
can: If I study, I can pass.（勉強すれば、合格できる。）これは潜在能力の話。能力はあるけど、本当にやるかな？
might: If I study, I might pass.（勉強すれば、合格するかも。）これは弱気な時。テストが難しいかも。ヤマが外れるかも。
これを Second Conditional（仮定法過去：If I studied, I would pass）と混同しないでね。Second Conditional は、想像上のことやあり得ない状況用だ。「宝くじが当たったら、プライベートアイランドを買うのに（If I won ..., I would ...）」みたいな。First Conditional（どの助動詞を使っても）は、未来の 現実的な可能性 の話だ。もし今実際に宝くじを手に持っているなら、First Conditional を使う。「もし当たったら、仕事辞めるかも（If I win, I might ...）。」デスクで仕事中にただ妄想してるだけなら、Second を使おう。この違いを知っておけば、現実に足をつけていられるし、少なくとも正確に妄想できるようになるよ。
Quick FAQ
First Conditional で could は使える？
使えるよ！ Could は can のもっと柔らかくて丁寧なバージョン、あるいは might よりも確信度が低いバージョンとして機能する。「お時間があれば、このExcelシート手伝っていただけますか？（If you have a minute, could you help ...）」みたいに。
may と might に違いはある？
最近のテキストや会話では、そんなにないね。May の方が少し堅苦しいけど、might を使ったからって文法警察に通報されることはないよ。
if 節の中に助動詞を入れてもいい？
基本的にはダメ。助動詞は結果節に入れるもの。「If I can go, I will be happy.」とは言わない。普通に「If I go...」か「If I am able to go...」と言うね。
アドバイスをすごく強く言いたい時は？
must を使おう。「火事を見つけたら、建物から出なければならない（you must exit）。」こういう時は should の出番じゃない。「燃えてるビルから出たほうがいいかもね（You should probably leave）」じゃ、緊急事態にしてはのんびりしすぎだ。
節（clause）を入れ替えたら意味は変わる？
全然！「I might go if it’s free」と「If it’s free, I might go」は全く同じ意味。コンマのルールだけ覚えておいて！ if が先ならコンマあり、if が真ん中ならコンマなしだよ。
Structure of First Conditional with Modals
| Clause Type | Verb Form | Example |
|---|---|---|
|
If-Clause (Condition)
|
Present Simple
|
If you study,
|
|
Main Clause (Result)
|
Modal + Base Verb
|
you can pass.
|
|
Negative If-Clause
|
Don't/Doesn't + Base
|
If he doesn't go,
|
|
Negative Main Clause
|
Modal + Not + Base
|
he might not see her.
|
|
Question Form
|
Modal + Subject + Base
|
Can we go if it stops?
|
Common Modal Contractions
| Full Form | Contraction | Usage |
|---|---|---|
|
Should not
|
Shouldn't
|
Very common
|
|
Cannot
|
Can't
|
Standard
|
|
Must not
|
Mustn't
|
Formal/Strong
|
|
Might not
|
N/A
|
Rarely contracted
|
Meanings
The first conditional with modals describes a possible future situation and its potential consequence, focusing on ability, permission, or advice rather than a guaranteed outcome.
Ability or Permission
Using 'can' to show what is possible or allowed if a condition is met.
“If we save enough money, we can buy a new car.”
“If you have a ticket, you can enter the stadium.”
Possibility or Uncertainty
Using 'might' or 'may' to show that the result is not 100% certain.
“If it gets colder, it might snow tonight.”
“If they don't hurry, they may miss the train.”
Advice or Suggestion
Using 'should' or 'must' to give recommendations based on a condition.
“If you feel sick, you should see a doctor.”
“If you want to lose weight, you must exercise more.”
Reference Table
| 助動詞 | 意味 | Example Sentence | 確実性のレベル |
|---|---|---|---|
|
can
|
可能性、能力、許可
|
If you practice, you can improve.
|
高い可能性／能力
|
|
might
|
弱い可能性、不確実性
|
If it rains, we might cancel the picnic.
|
低〜中程度の可能性
|
|
should
|
アドバイス、勧め、軽い義務
|
If you're tired, you should rest.
|
勧め／提案
|
|
can't
|
不可能、できない
|
If it's locked, we can't get in.
|
できないことの確実性が高い
|
|
might not
|
弱い否定の可能性
|
If he's busy, he might not come.
|
低〜中程度の否定の可能性
|
|
shouldn't
|
否定のアドバイス、勧め
|
If you're sick, you shouldn't go out.
|
否定の勧め
|
フォーマル度スペクトル
If you are available, we might convene this afternoon. (Scheduling)
If you are free, we can meet this afternoon. (Scheduling)
If you're free, we could hang out later. (Scheduling)
If you're down, we can link up later. (Scheduling)
助動詞を使うFirst Conditional: 核となる考え
If節（条件）
- 現在形 e.g., If it rains... If she studies...
主節（結果）
- 助動詞 + 動詞の原形 e.g., ...we can go. ...you might pass. ...you should rest.
助動詞とその意味
- Can 能力／許可／可能性
- Might 弱い可能性／不確実性
- Should アドバイス／勧め
適切な助動詞の選び方
助動詞を使うFirst Conditional フローチャート
未来の現実的な可能性について話していますか？
能力、許可、または強い可能性を表したいですか？
弱い可能性や不確実性を表したいですか？
アドバイスや勧めをしたいですか？
First Conditional 助動詞の使用ケース
アドバイス＆提案
- • If you're hungry, you should eat.
- • If you need help, you should ask.
未来の可能性
- • If it rains, we might stay in.
- • If he calls, I might answer.
能力＆機会
- • If I save, I can travel.
- • If you finish, you can leave.
許可
- • If you ask, you can go.
- • If you clean, you can play.
レベル別の例文
If I have money, I can buy a pizza.
If I have money, I can buy a pizza.
If you are happy, you can dance.
If you are happy, you can dance.
If it is hot, we can go to the beach.
If it is hot, we can go to the beach.
If you help me, I can finish.
If you help me, I can finish.
If you feel sick, you should stay in bed.
If you feel sick, you should stay in bed.
If he calls you, you should answer.
If he calls you, you should answer.
If we don't hurry, we might be late.
If we don't hurry, we might be late.
If you find my keys, can you tell me?
If you find my keys, can you tell me?
If the weather improves, we might go for a hike.
If the weather improves, we might go for a hike.
If you want the job, you must prepare for the interview.
If you want the job, you must prepare for the interview.
If they offer a discount, I may buy the laptop.
If they offer a discount, I may buy the laptop.
If you don't like the food, you shouldn't eat it.
If you don't like the food, you shouldn't eat it.
If the company expands, we could potentially hire more staff.
If the company expands, we could potentially hire more staff.
If you encounter any issues, you ought to contact support immediately.
If you encounter any issues, you ought to contact support immediately.
If the results are inconclusive, we might have to repeat the experiment.
If the results are inconclusive, we might have to repeat the experiment.
If she decides to resign, it could cause significant problems.
If she decides to resign, it could cause significant problems.
If the legislation passes, it might well redefine the industry.
If the legislation passes, it might well redefine the industry.
If we are to succeed, we must remain vigilant at all times.
If we are to succeed, we must remain vigilant at all times.
If the market remains volatile, investors should exercise extreme caution.
If the market remains volatile, investors should exercise extreme caution.
If you happen to see her, you might mention the upcoming gala.
If you happen to see her, you might mention the upcoming gala.
If the hypothesis holds true, we can deduce that the initial assumptions were flawed.
If the hypothesis holds true, we can deduce that the initial assumptions were flawed.
If one is to master the craft, one must be prepared for years of toil.
If one is to master the craft, one must be prepared for years of toil.
If the negotiations fail, the repercussions could be felt for decades.
If the negotiations fail, the repercussions could be felt for decades.
If you should find yourself in need of counsel, my door remains open.
If you should find yourself in need of counsel, my door remains open.
間違えやすい
Learners mix up 'If I win, I can' (possible) with 'If I won, I could' (imaginary).
Using 'will' when you mean 'ability'.
Learners think they are completely different rules.
よくある間違い
If it will rain, I can stay.
If it rains, I can stay.
If I see her, I can to tell her.
If I see her, I can tell her.
If he go, I might go.
If he goes, I might go.
I can go if it will be sunny.
I can go if it is sunny.
If you are tired, you should to rest.
If you are tired, you should rest.
If I have time, I might will go.
If I have time, I might go.
If it rains, we can't to play.
If it rains, we can't play.
If you would like, I can help.
If you like, I can help.
If I might see him, I will tell him.
If I see him, I might tell him.
If you go there, you must to be careful.
If you go there, you must be careful.
If the weather will be good, we can go.
If the weather is good, we can go.
文型パターン
If I ___, I can ___.
If you ___, you should ___.
If they ___, we might ___.
If the ___ doesn't ___, we must ___.
Real World Usage
If you're free later, we can grab coffee.
If I am hired, I can start immediately.
If the flight is delayed, we might miss our connection.
If you have gluten-free bread, I should try it.
If you like this video, you should subscribe!
If the pain continues, you must call me.
変化をつけよう！
If you practice, you can improve.
If節には「will」を使わないで！
If it rains, we might cancel the picnic.
微妙な違いを知ろう
丁寧なアドバイス
If you want to learn English faster, you should practice every day.
Smart Tips
Use 'might' instead of 'will'. It makes the request feel less like a demand.
Read the sentence aloud. If you naturally pause after the first part, you probably need a comma.
Use 'must' instead of 'should' to show that the condition is vital.
Check if 'will' is in the 'if' part. If it is, delete it!
発音
Modal Reduction
In fast speech, 'can' is often reduced to /kən/ (kun), while 'can't' is stressed with a clear /æ/ sound.
The 'If' Schwa
The word 'if' is often very short and unstressed.
Conditional Rise-Fall
If it rains (rise), we can stay home (fall).
The rising tone on the if-clause signals that the thought is incomplete.
暗記しよう
記憶術
If the Present is the key, the Modal sets the possibility free.
視覚的連想
Imagine a fork in the road. The 'If' is the start of the road. 'Will' is a straight line, but 'Might' is a foggy path, and 'Should' is a signpost giving advice.
Rhyme
If you use 'if', don't use 'will', or your grammar grade will take a spill!
Story
A traveler stands at a gate. 'If I have the key (Present), I can enter (Modal).' He isn't sure if he has it, so he says 'If I find it, I might enter.'
Word Web
チャレンジ
Write 3 sentences about your plans for tomorrow using 'if' and three different modals (can, might, should).
文化メモ
British speakers often use 'might' or 'could' to sound more polite and less direct than 'will'.
Americans frequently use 'should' for strong recommendations in conditional sentences.
Use of 'might' is very common to express a laid-back, non-committal attitude.
Conditionals in English evolved from Old English 'gif' (if), which set up a hypothetical premise.
会話のきっかけ
If you win the lottery, what can you buy for your family?
If it rains this weekend, what might you do instead of going out?
If you get a promotion, how might your life change?
If you could move to any country, where should you go for the best food?
日記のテーマ
よくある間違い
Test Yourself
If you study consistently, you ___ definitely improve your English.
Find and fix the mistake:
If she will arrive late, we might start dinner without her.
Choose the correct sentence:
Score: /3
練習問題
8 exercisesIf it ___ (be) sunny tomorrow, we ___ (can / go) to the park.
Find and fix the mistake:
If you will study hard, you might pass the exam.
If you feel tired, you ___ take a nap.
might / if / late / we / be / hurry / don't / we
Translate the sentence.
1. If it rains... 2. If you are hungry... 3. If you win...
Choose the formal version.
If he ___ (not / arrive) soon, we ___ (must / leave) without him.
Score: /8
Practice Bank
12 exercisesIf you want good grades, you ___ listen carefully in class.
If we will leave soon, we can avoid the traffic.
Choose the correct sentence:
Translate into English: 'Si hace sol, podríamos ir a la playa.'
Arrange these words into a sentence:
Match the 'if' clauses with their likely results:
If I get a promotion, I ___ finally afford a bigger apartment.
Translate into English: 'Si tienes dudas, deberías preguntar al profesor.'
If she practice more, she might to win the competition.
Arrange these words into a sentence:
Which sentence is correct?
Connect the clauses:
Score: /12
よくある質問 (8)
Yes, you can use `could` to show a theoretical ability or a very polite suggestion, though it's more common in the second conditional. In the first conditional, it means 'it is possible that we will be able to'.
In English, the `if-clause` sets the condition, and we use the present tense to represent that condition as a fact or a real possibility. Using `will` there is redundant and grammatically incorrect in standard English.
In first conditionals, they are interchangeable. `May` is more formal and slightly more certain, while `might` is more common in conversation and suggests a slightly lower chance.
Only if the `if-clause` comes first. If you say 'I can help you if you want,' no comma is needed.
Yes, but it's very strong. Use `should` for friendly advice and `must` for things that are absolutely necessary, like 'If you drive, you must have a license.'
Yes, you can use the Present Continuous in the if-clause if the action is happening now or is a fixed plan. 'If you're going to the store, can you buy milk?'
It's rare but possible when talking about present ability as a condition. 'If you can play the piano, you can join the band.'
Then you need a 'Mixed Conditional,' which is a more advanced rule. First conditionals only deal with future results.
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
Si + Presente, Poder/Deber + Infinitivo
Spanish speakers often try to use the future in the 'if' clause when speaking English.
Si + Présent, Pouvoir/Devoir + Infinitif
French learners often struggle with the 'no will' rule because they use the future more flexibly.
Wenn + Präsens, Modalverb
German word order (verb at the end of the if-clause) is the main hurdle.
~tara / ~ba + modal equivalent
Japanese doesn't have a direct 'if' word that functions exactly like the English one.
In / Idha + Present
The sequence of tenses in Arabic is quite different from English.
Ruguo... jiu...
Chinese has no verb conjugation, so the 'Present Simple' rule is purely about word order.
Learning Path
Prerequisites
Learn These First
Related Grammar Rules
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