Chapter in 30 Seconds
Master the art of speculating about the past and predicting the future with confidence.
- Analyze past events using modal perfect structures.
- Express strong beliefs and logical deductions about reality.
- Utilize probability markers to sound like a native speaker.
学べること
こんにちは！この章では、英語の表現力を一気にネイティブレベルへと引き上げる「助動詞」の深い世界をマスターします。B2レベルの皆さんなら、単に事実を述べるだけでなく、「〜だったに違いない」「〜だったかもしれない」といった、過去に対する繊細な推測や論理的な分析を英語で表現したいですよね。ここでは、must have や can't have を使った確信度の高い推論から、could have による「あり得たかもしれない過去」の話し方まで、11の重要なルールをじっくり学びます。例えば、友人がなぜパーティーに来なかったのかを分析したり、映画の伏線について議論したりする場面で、あなたの意見にぐっと説得力が生まれます。さらに、had better や ought to を使った的確なアドバイスや、would rather による洗練された意思表示も習得。この章を終える頃には、事実の裏側にある可能性や確信を自由自在に操れるようになり、より知的で深みのある英会話が楽しめるようになりますよ。さあ、一緒に表現の幅を広げましょう！
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形式的な未来と規則 (Shall)Shallは、未来の行動や規則に、フォーマルさ、義務感、または強い決意のニュアンスを加えることができます。「Formal」「Obligation」「Determination」の3つのキーワードで覚えておきましょう。
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英語の助動詞: Had Better (アドバイスと警告)緊急の忠告や警告には
had betterを使います。常に動詞の原形が続き、toは不要です。 -
好みを表明する: Would Rather「Would rather」は、自分や相手の行動について、丁寧かつ明確に好みを伝えるための「魔法の表現」です。
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過去の可能性：〜できたのに (Could Have)「could have」は、過去に「possible in the past」だったけれど、「did not occur」した行動について話す時に使います。
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過去の推測：Might Have（〜したかもしれない）「might have」は、過去に何かが「起こったかもしれない」と、あなたが完全に確信しているわけではないときの「推測」を表す魔法のフレーズです。
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過去の推測: Must Have + V3証拠に基づいて過去の状況について「must have + V3」を使って『確信』を持って『論理的な推測』をしましょう。これがあなたの表現に深みを与えます。
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過去の強い不信 (Can't Have + V3)過去の出来事に対して「絶対にありえない！」と論理的に確信して否定するときは "can't have + V3" を使いましょう。
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逃したチャンス：「Could have」の使い方（実現しなかった可能性）「could have」を使いこなせば、過去の選択や「実現しなかった可能性」について、もっとはっきり気持ちを伝えられるようになりますよ。これはまさに「過去の可能性」を語るための「魔法のフレーズ」です！
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Ought To: 助言と義務「ought to」は、良心に基づいたアドバイスや、当然すべきことを伝える魔法の言葉です。「
right(正しいこと)」「expected(期待されること)」を伝えるときに使いますよ。 -
Speculation and Deduction: Must Be, Can't Be, Might Be (Present)Use must be, can't be, could be, and might be to make deductions about present situations. Must be = almost certain; can't be = impossible; might/could be = possible.
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Likely, Unlikely, Bound To, Certain To: Expressing ProbabilityBound to = almost certain to happen. Likely/unlikely = probable/improbable. Certain to = guaranteed. These adjectives follow be and precede infinitives.
Learning Objectives
By the end of this chapter, you will be able to:
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1
By the end you will be able to: describe past events that might have occurred using perfect modals.
チャプターガイド
Overview
shall for formal future plans or polite offers, how had better gives urgent advice, and why would rather is perfect for stating preferences. We'll also explore ought to for moral obligations.How This Grammar Works
I could have gone to the party, but I was too tired.This shows a missed chance or an unrealized possibility.
The ground is wet. It must have rained last night.Conversely, to express strong past disbelief – a near 99% certainty that something *didn't* happen – use can't have + past participle.
Guests shall not smoke indoors), or for polite offers/suggestions (typically British English):
Shall I open the window for you?. For urgent advice where ignoring it leads to negative consequences, use had better: "You had better leave now, or you'll miss your flight.
To state a preference in a specific situation, would rather + base verb is perfect:I would rather stay home tonight than go out.
Finally, ought to + base verb conveys moral advice or logical expectation, offering a slightly stronger or more meaningful alternative to should: You ought to apologize; what you said was hurtful."
Common Mistakes
- 1✗ I must went home early.
must, might, could, can't are followed by have + the past participle (V3) form of the main verb, not the base form.- 1✗ He didn't arrive; he might not have seen my message.
might not have expresses a possibility of something *not* happening, couldn't have implies stronger impossibility or unlikelihood (similar to can't have but often used for a specific past inability). Be clear about your degree of certainty.- 1✗ I had better to study for the exam.
Had better is followed directly by the base form of the verb, without to.
Real Conversations
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B
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A
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We could have gone to that concert, but tickets sold out. I would rather watch a movie at home than just sit around doing nothing.
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Good idea. What movie shall we watch?
Quick FAQ
What's the difference between might have and must have when guessing the past?
Might have indicates a possibility, meaning you're unsure (e.g.,
She *might have* left her keys).
Must have indicates strong certainty based on evidence (e.g., The lights are on, so she *must have* arrived).
Can could have be used for both possibility and missed chances?
Yes.
I *could have* won the lottery(missed chance/unrealized possibility) and
He *could have* been sick yesterday(past possibility/speculation) are both correct uses.
Is "can't have" always about impossibility?
Yes, "can't have" + past participle expresses a very high degree of certainty that something *did not* or *could not have* happened. It's a strong rejection of a past possibility.
When should I use ought to instead of should?
Ought to often carries a slightly stronger sense of moral obligation, logical expectation, or what is 'right', compared to the more general advice of should. While often interchangeable, ought to can feel a bit more formal or weighty.
Cultural Context
Shall is notably more common in British English for polite offers (Shall I get it?) and formal/legal contexts, while less frequently used in everyday American English, where
will or should I are preferred. Had better is universally understood but can sound a little direct or even like a veiled threat if not used carefully, especially in informal settings.must have, might have, could have, and can't have are quite consistent across all major English dialects, serving as reliable tools for discussing past events with varying degrees of certainty. Mastering these nuances will make your communication sound much more natural.重要な例文 (8)
You'd better submit that assignment by midnight, or you'll lose points.
夜中までにその課題を提出した方がいいよ、さもないと減点されちゃうから。
英語の助動詞: Had Better (アドバイスと警告)We had better not forget to buy milk on the way home.
家に帰る途中で牛乳を買うのを忘れない方がいいよ。
英語の助動詞: Had Better (アドバイスと警告)I'd rather have a quiet night in than go to a crowded party.
賑やかなパーティーに行くよりは、静かに家で過ごしたいです。
好みを表明する: Would RatherWould you rather study now or take a break and study later?
今勉強したいですか、それとも休憩してから後で勉強したいですか？
好みを表明する: Would RatherI could have stayed in bed all day, but I decided to go to the gym.
一日中ベッドにいてもよかったのですが、ジムに行くことにしました。
過去の可能性：〜できたのに (Could Have)You could have liked my photo on Instagram, it took me an hour to edit!
私のインスタの写真、いいねしてくれてもよかったのに！編集に1時間もかかったんだよ！
過去の可能性：〜できたのに (Could Have)ヒントとコツ (4)
迷ったら「Will」を使いましょう
短縮形はあなたの味方です！
I'd better、you'd better、we'd better など短縮形を使うと、I had better のように完全に言うよりもずっと自然に聞こえますよ！積極的に使ってみましょう。「I'd better go now.」短縮形を使いこなそう！
「Could Of」という落とし穴！
I could have gone.
重要な語彙 (5)
Real-World Preview
The Mystery Meeting
Review Summary
- Must have + V3
よくある間違い
People often confuse 'have' with the sound of 'of' in contractions.
Modals are followed by the base form 'have', never 'has'.
Again, use 'have' after modal perfects regardless of the subject.
このチャプターのルール (11)
Next Steps
You have mastered complex past speculation! Take a moment to celebrate this achievement.
Write a 5-sentence mystery story using 3 modal perfects.
クイック練習 (10)
Choose the correct sentence:
frontend.learn_grammar.from_rule: 過去の推測: Must Have + V3
All employees ___ adhere to the new safety regulations.
frontend.learn_grammar.from_rule: 形式的な未来と規則 (Shall)
I ___ have bought that laptop, but I saved my money instead.
frontend.learn_grammar.from_rule: 過去の可能性：〜できたのに (Could Have)
Find and fix the mistake:
It is unlikely that he will to come.
frontend.learn_grammar.from_rule: Likely, Unlikely, Bound To, Certain To: Expressing Probability
I'd rather ___ a book than watch TV.
frontend.learn_grammar.from_rule: 好みを表明する: Would Rather
Find and fix the mistake:
He ought study harder for his final exams.
frontend.learn_grammar.from_rule: Ought To: 助言と義務
Find and fix the mistake:
He mustn't be the thief.
frontend.learn_grammar.from_rule: Speculation and Deduction: Must Be, Can't Be, Might Be (Present)
Choose the correct sentence:
frontend.learn_grammar.from_rule: Ought To: 助言と義務
Find and fix the mistake:
They could have went to the concert last night.
frontend.learn_grammar.from_rule: 過去の可能性：〜できたのに (Could Have)
Find and fix the mistake:
I will forever uphold the values of this institution.
frontend.learn_grammar.from_rule: 形式的な未来と規則 (Shall)
Score: /10
よくある質問 (6)
had better は、何かをすることが非常に勧められる、または推奨されるという意味で、しばしばその行動が取られない場合に否定的な結果が生じるという暗黙の警告を伴います。should よりも強いと考えると良いでしょう。「You'd better listen to me.」had が含まれていますが、had better は**常に現在または未来**を指します。今すぐ、または近いうちに起こる必要がある行動に関するアドバイスや警告に使われ、過去の出来事には使いません。「We'd better hurry, or we'll be late for the meeting.」
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