B1 · 中級 チャプター 31

「かもしれない」の先へ！確信度を操る推測のマスター講座

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51 例文
6 分
このチャプターのルール クイック練習

Chapter in 30 Seconds

Master the art of expressing uncertainty and logical deductions with professional precision.

  • Differentiate between weak and strong possibilities using modal verbs.
  • Make logical deductions based on evidence using 'must' and 'can't'.
  • Use advanced probability adjectives and adverbs to sound more natural.
Stop guessing, start expressing levels of certainty.

学べること

日常会話で「たぶん…かな？」とあいまいに言うだけでなく、自分の「確信の度合い」を正確に伝えたいと思ったことはありませんか？この章では、そんな「推測」の表現力を一気に引き上げます。まずは基本の may や might で「〜かもしれない」という可能性を表現。さらに、根拠に基づいて「〜に違いない（must）」や「そんなはずはない（can't be）」と断定する論理的な推論も学びます。さらに一歩進んで、より自信のある may well や、確実性の高い bound to など、ネイティブが使い分ける繊細なニュアンスもマスターしましょう。例えば、鍵を失くした時に「絶対ここに置いてあるはずなのに！」と論理的に考えたり、会議で「プロジェクトはまず間違いなく成功するでしょう」と予測を伝えたりする場面。こうした「可能性の階段」を自由に上り下りできるようになると、あなたの英語はより知的で信頼感のあるものに変わります。さあ、一緒に表現の幅を広げましょう！

Learning Objectives

By the end of this chapter, you will be able to:

  1. 1
    By the end you will be able to: describe a 30-50% chance of an event happening using may or might.
  2. 2
    By the end you will be able to: conclude that something is definitely true or false based on evidence.
  3. 3
    By the end you will be able to: rank different outcomes from 'unlikely' to 'bound to' using non-modal structures.

チャプターガイド

Overview

As a B1 English learner, you're moving beyond basic communication and starting to express more nuanced ideas. This is where understanding English possibility and probability becomes incredibly useful! Imagine you're making plans, discussing news, or even just wondering about the weather – knowing how to express how likely something is can really boost your confidence and make your English sound much more natural.
This chapter will equip you with essential tools to talk about uncertainty and make logical deductions.
We'll explore how to use modal verbs like may and might to express things that are simply possible, and how must helps you sound confident about a logical conclusion. You'll also learn handy phrases like may well and might well to express a higher degree of probability. By mastering these concepts, you'll be able to discuss potential outcomes, explain why you think something is true, and even confidently state when something just can't be!
These are all key skills for navigating a wide range of everyday conversations at the B1 English grammar level.
Being able to differentiate between something that *might* happen and something that *must* be true based on evidence will help you communicate more precisely. It's about adding depth to your English, allowing you to share your thoughts and reasoning in a clear and convincing way. Get ready to discuss possibilities and probabilities like a pro!

How This Grammar Works

Let's break down the core grammar rules for expressing possibility and probability in English. We use modal verbs to do this, and they always precede a base verb (the infinitive without 'to').
When you're talking about something that is possible, but not certain, you'll use may or might. They are largely interchangeable for present or future possibility. For example,
It may rain later
means there's a chance of rain.
Similarly,
She might be at the library
suggests it's a possibility, but you're not sure. These express general uncertainty or a 'maybe' situation.
Now, if you're quite sure about something based on evidence or logic, you use must. This isn't about obligation; it's about making a logical deduction. If your friend has been studying all night, you could say,
She must be tired.
You're almost certain based on the clues.
This is called the epistemic must. The evidence makes it highly probable.
To add a bit more strength to your predictions, you can use may well or might well. These phrases indicate that something is quite likely because it makes good sense or there are strong reasons for it. For instance, "If he doesn't study, he may well fail the exam" implies that it's a very probable outcome given his actions.
It's stronger than just may or might alone, suggesting a reasonable expectation.
Finally, when you're absolutely certain that something is logically impossible, you use can't. For example, if you see someone enter a room and then immediately leave through the same door, you could say, "She can't be in the room anymore." The evidence tells you it's impossible. It's the opposite of must for logical deduction.
These structures build on each other, allowing you to express varying degrees of certainty.

Common Mistakes

  1. 1✗ Using 'must' for permission instead of logical deduction in this context.
✓ He must be home, his car is in the driveway. (Correct: Logical deduction)
✗ You must go to the party. (Incorrect for probability; this is obligation. For possibility, you might say
You might go to the party if you want.
)
*Explanation:* Remember that the 'must' we're focusing on here is for making a logical guess, not for giving orders or saying something is required.
  1. 1✗ Confusing 'may' and 'might' for past possibility.
✓ She may have forgotten her keys. (Correct for past possibility)
✗ She might forget her keys yesterday. (Incorrect: 'Might' for past possibility needs 'have' + past participle)
*Explanation:* For past possibility or probability, you need to use may have + past participle or might have + past participle. The chapter focuses on present/future, but this is a common extension.
  1. 1✗ Using 'cannot' instead of 'can't' for logical impossibility in informal contexts.
✓ That can't be true! (Correct: Common and natural)
✗ That cannot be true! (Less natural in everyday, conversational English for this specific meaning, though grammatically correct)
*Explanation:* While 'cannot' is grammatically fine, 'can't' is much more common and natural when expressing logical impossibility in conversational English.

Real Conversations

A

A

The lights are off in John's office. He usually works late.
B

B

He must have left already. It's almost 7 PM.
A

A

Do you think Sarah will come to the party?
B

B

She said she was busy, so she might not make it. But she may well surprise us if her meeting finishes early.
A

A

I can hear music from next door.
B

B

Oh, that can't be my neighbour. He's on holiday in Spain this week!

Quick FAQ

Q

Can I use 'may' and 'might' interchangeably for possibility?

Yes, in most cases for present and future possibility, may and might are interchangeable. Some people feel 'might' expresses a slightly weaker possibility, but the difference is very subtle and often not significant in everyday conversation.

Q

How is 'must' for possibility different from 'must' for obligation?

Must for possibility (epistemic) means

I am almost certain based on evidence
(e.g.,
He must be rich; he drives a fancy car.
). Must for obligation means
It is necessary or required
(e.g.,
You must finish your homework.
). The context makes the meaning clear.

Q

Is 'may well' much stronger than 'may'?

Yes, may well expresses a higher degree of probability than just may. It suggests that something is quite likely because there's a logical reason or expectation for it to happen. It's like saying "it's very likely or it's probable."

Q

When should I use 'can't' instead of 'won't be able to' for impossibility?

Use can't when you're making a logical deduction that something is impossible based on facts or evidence ("That can't be true, I saw it myself!"). Use 'won't be able to' for future inability or lack of opportunity ("I won't be able to come tomorrow, I have an appointment.").

Cultural Context

Native English speakers use these modal verbs constantly to soften statements, express uncertainty, and convey different levels of conviction. In casual conversation, you'll hear might and can't a lot, as they add a natural flow. Must for deduction is also very common.
While may well and might well are perfectly natural, they tend to be slightly more formal or used when explaining a reasoned prediction. There aren't significant regional differences in the core usage of these modals, but the frequency of their use may vary slightly between individuals.

重要な例文 (8)

1

I `may go` to the gym after work, if I'm not too tired.

仕事の後、疲れていなかったらジムに行くかもしれません。

英語の可能性: May と Might
2

They `might be` stuck in traffic, which is why they're late.

彼らは渋滞にはまっているのかもしれません、だから遅れているんです。

英語の可能性: May と Might
3

Look at all the snow! It `must be` freezing outside.

見て、この雪！外はきっと凍えるほど寒いだろうね。

「Must」を使った論理的な推測（認識的）
4

He's wearing a doctor's coat. He `must be` a doctor.

彼は医者の白衣を着ている。きっと医者だろう。

「Must」を使った論理的な推測（認識的）
5

She **may well pass** the exam; she studied all week.

彼女は試験に合格する可能性が高いでしょう。一週間ずっと勉強していましたから。

可能性ブースター: May Well & Might Well
6

The package **might well arrive** tomorrow, as it shipped yesterday.

荷物は明日届く可能性が高いでしょう。昨日発送されましたからね。

可能性ブースター: May Well & Might Well
7

That pizza place `can't be closed` already, it's only 8 PM!

あのピザ屋さん、もう閉まってるはずないよ、まだ夜8時だよ！

論理的な不可能性（ありえない！）
8

My internet `couldn't have gone out`. I just paid the bill yesterday.

うちのインターネットが使えなくなったはずがないよ。昨日ちょうど料金を払ったばかりだもん。

論理的な不可能性（ありえない！）

ヒントとコツ (4)

💡

丁寧な提案に使う

友達に「これ試してみたらどう？」と優しく提案する時、「You might want to consider this」と言うと、押し付けがましくなく、協力的な印象になるよ。
frontend.learn_grammar.from_rule: 英語の可能性: May と Might
💡

証拠を探そう！

「must」を使って推測する前には、必ず確かな証拠があるか確認してね。証拠が強ければ強いほど、「must」を使う自信が持てるよ。
The ground is wet. It must have rained.
frontend.learn_grammar.from_rule: 「Must」を使った論理的な推測（認識的）
💡

予測に自信をプラス！

「May well」や「might well」を使うと、あなたの予測に「確信度」が加わります。例えば、友達が「あのチームは強いから、きっと勝つよ」って言っている時、その「きっと」の気持ちをより説得力のある形で伝えられます。「They may well win the game.」
frontend.learn_grammar.from_rule: 可能性ブースター: May Well & Might Well
💡

逆を考えてみよう

「きっと〜に違いない (must be)」と強く推測する時の反対だと思ってね。例えば「He must be rich」の反対は「He can't be poor」みたいに、論理的なつながりが分かりやすくなるよ。
frontend.learn_grammar.from_rule: 論理的な不可能性（ありえない！）

重要な語彙 (6)

Evidence facts or signs that show something is true Likelihood the chance that something will happen Certain completely sure about something Possible able to be done or happen Impossible not able to occur or exist Predict to say what will happen in the future

Real-World Preview

coffee

Solving an Office Mystery

Review Summary

  • Subject + may/might + base verb
  • Subject + must + base verb
  • Subject + can't + base verb

よくある間違い

In English, we do not use 'must not' for logical deductions. We use 'can't' to say something is logically impossible.

Wrong: It must be not true.
正解: It can't be true.

Modal verbs like 'might' never take an 's' in the third person singular.

Wrong: He mights come to the party.
正解: He might come to the party.

Adverbs of probability like 'probably' usually go after the first auxiliary verb or before the main verb.

Wrong: Probably I will see you later.
正解: I will probably see you later.

Next Steps

You've unlocked a new level of English! Being able to speculate and deduce makes your conversations much more interesting. Keep practicing those 'must be' moments!

Look out the window and make 5 'must be' and 5 'might be' observations about people you see.

Continue to: ネイティブの表現力を手に入れる！自然な「言葉のセット」完全攻略

クイック練習 (10)

論理的な不可能性を表す正しい形を選んでください。

He's only 16, so he ___ a licensed driver yet.

✓ Correct! ✗ Not quite. Correct answer: can't be
彼は16歳なので、まだ運転免許を持っているのは論理的に不可能です（ほとんどの地域で）。「Can't be」はこの不可能性を表現します。

frontend.learn_grammar.from_rule: 論理的な不可能性（ありえない！）

正しい形を選んで文を完成させましょう。

She ___ be at the library right now, I'm not sure.

✓ Correct! ✗ Not quite. Correct answer: may
「May」は助動詞なので形は変わらないよ。動詞の原形（be）が続くんだ。

frontend.learn_grammar.from_rule: 英語の可能性: May と Might

論理的な推測を完成させるために、正しい形を選びましょう。

The lights are off and the door is locked. She ___ asleep.

✓ Correct! ✗ Not quite. Correct answer: must be
現在の論理的な推測には、「must」の後に動詞「to be」の原形を使います。

frontend.learn_grammar.from_rule: 「Must」を使った論理的な推測（認識的）

過去の出来事についての論理的な推測を正しく表現している文を選びましょう。

Choose the correct sentence:

✓ Correct! ✗ Not quite. Correct answer: They must have missed the bus.
過去の出来事についての論理的な推測には、「must have」+過去分詞の構造が正しいです。

frontend.learn_grammar.from_rule: 「Must」を使った論理的な推測（認識的）

Choose the correct sentence.

Which is correct?

✓ Correct! ✗ Not quite. Correct answer: I will probably go.
Probably before verb.

frontend.learn_grammar.from_rule: Probability: Likely, Unlikely, Bound To, Definitely, Probably

文中の間違いを見つけて修正してください。

Find and fix the mistake:

They mustn't be home. Their car isn't in the driveway.

✓ Correct! ✗ Not quite. Correct answer: They can't be home. Their car isn't in the driveway.
ここでは「mustn't be」は正しくありません。話し手は証拠（車がないこと）に基づいて論理的な推測をしているので、論理的な不可能性を表す「can't be」が適切な選択です。

frontend.learn_grammar.from_rule: 論理的な不可能性（ありえない！）

正しい文を選んでください。

Choose the correct sentence:

✓ Correct! ✗ Not quite. Correct answer: He may well succeed.
このフレーズの正しい語順は「助動詞 + well + 動詞の原形」です。「well」は助動詞の直後に来ます。

frontend.learn_grammar.from_rule: 可能性ブースター: May Well & Might Well

文中の間違いを見つけて修正しましょう。

Find and fix the mistake:

They might to forget about our meeting.

✓ Correct! ✗ Not quite. Correct answer: They might forget about our meeting.
助動詞（might）の後には、動詞の原形（forget）が「to」なしで直接続くんだ。

frontend.learn_grammar.from_rule: 英語の可能性: May と Might

間違いを見つけて直してください。

Find and fix the mistake:

If you don't save, you might as well run out of money.

✓ Correct! ✗ Not quite. Correct answer: If you don't save, you might well run out of money.
ここでは、貯金しないことの結果としてお金がなくなる可能性が高いことを示す「might well」が必要です。「might as well」は、それを選択肢として提案する意味になります。

frontend.learn_grammar.from_rule: 可能性ブースター: May Well & Might Well

Fill in the blank.

It is ___ to rain.

✓ Correct! ✗ Not quite. Correct answer: likely
Likely takes 'to'.

frontend.learn_grammar.from_rule: Probability: Likely, Unlikely, Bound To, Definitely, Probably

Score: /10

よくある質問 (6)

何かが「可能である」とか「起こりそうだ」という、確実ではないことを表現するのが主な考え方だよ。断定せずに推測したり、可能性を話したりする時に使うんだ。例えば、「It may rain later」とか「She might be busy」のようにね。
現代のほとんどの文脈で、可能性を表現するなら、はい、ほとんど交換可能だよ。「might」の方が少し確率が低いことを示唆することもあるけど、その違いはとても微妙で、日常会話ではあまり意識されないことが多いんだ。
これは、持っている証拠に基づいて、強く確信を持った推測をすることだよ。「Xがあるから、Yが『must be』真実だ」と、それが唯一の論理的な結論だと主張しているんだ。
The lights are off, so he must be asleep.
とても確信があるよ！95～99%くらいの確率だと思ってね。証拠が非常に強くて、その結論がほとんど否定できないように思えるときに「must」を使うんだ。
「May well」は、「〜する可能性が非常に高い」とか、「〜する公算が大きい」という意味です。ただの「may」よりも確信度が高く、その可能性が高まる論理的な理由があることを示唆します。例えば、友達が「彼女は一週間ずっと勉強してたから、試験に合格する可能性が高いだろうね」って言いたい時、「She may well pass the exam.」のように使えます。
高い可能性を表す点では、ほとんど同じように使えます。「Might well」の方が、時に少し控えめなニュアンスだったり、仮定の状況で使われたりすることもありますが、どちらも「非常に高い可能性」という核となる意味は変わりません。例えば、「The package might well arrive tomorrow.」のように使います。
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