Grammar Rule in 30 Seconds
Use 'Supposing' to invite someone to imagine a hypothetical situation, often replacing 'if' for more dramatic or speculative effect.
- Use 'Supposing' + Past Tense for unlikely present/future scenarios: 'Supposing we lost everything?'
- Use 'Supposing' + Past Perfect for impossible past scenarios: 'Supposing you hadn't met him?'
- Always follow the 'Supposing' clause with a question or a result clause: 'Supposing it rains, what then?'
Overview
if を使うだけでは不十分です。日常会話からビジネス、アカデミックな議論に至るまで、ネイティブスピーカーは状況の「仮定」や「推測」の度合いに応じて、語彙を巧みに使い分けています。その中でも、特に知的で戦略的な響きを持つのが、今回詳しく解説する supposing です。supposing は、単なる条件の提示を超えて、聞き手や読み手を「思考実験（Thought Experiment）」へと誘う強力なツールです。日本語で言えば「もし〜だと仮定してみたら」「仮に〜という状況を想定すると」といった、より能動的で探索的なニュアンスを含みます。if が「もしAならB」という単純な因果関係を示すのに対し、supposing は「今からあるシナリオを提示します。それを事実だと受け入れた上で、一緒にその先を考えてみましょう」という、相手の想像力への働きかけが含まれているのです。supposing の文法的な仕組みから、if との決定的な違い、そして日本人が陥りやすいミスまで、上級者が知っておくべきエッセンスを網羅的に解説します。これをマスターすることで、あなたの英語はより説得力を増し、複雑なシチュエーションでの議論や提案が格段にスムーズになるはずです。supposing は文法的には「従属接続詞（Subordinating Conjunction）」、あるいは分詞構文から派生した前置詞的な役割を果たす語として機能します。その本質は、特定の前提（Premise）を一時的に「事実」として設定し、その結果として生じる事象を考察することにあります。supposing を使う際、最も重要なのは、その後に続く節の時制が、メインの節（帰結節）の時制と論理的に一致していなければならないという点です。これは、私たちが学校で学んだ「仮定法（Subjunctive Mood）」のルールがそのまま適用されることを意味します。supposing の背後には常に What if...?（もし〜だったらどうなるだろう？）という問いが隠されています。単なる事実の確認ではなく、未知の領域や、現実とは異なる可能性を「あえて」探るという心理的プロセスが反映されているのです。例えば、ビジネスの戦略会議で If we fail... と言うよりも、Supposing we failed... と言う方が、より深く、より慎重にそのリスクを検討しようという姿勢が伝わります。これは、話し手がその状況を一つの「仮説」として提示し、聞き手にその思考プロセスへの参加を求めているからです。supposing を使った文の構成は、基本的には if 節と同じパターンに従います。大きく分けて、以下の3つの型（Type 1, 2, 3）と、名詞句を伴う特殊な形があります。- Type 1: 未来の可能性（Future Possibility）
- 構成:
Supposing+ 現在形 (条件), 未来形 (will+ 動詞の原形) (結果) - 役割: 十分に起こり得る未来の状況を想定し、その結果を予測します。
- 例文:
Supposing you finish the report by noon, will you be able to join the meeting?（もし正午までにレポートが終わるとしたら、会議に参加できますか？）
- Type 2: 現在・未来の反事実（Unreal Present/Future）
- 構成:
Supposing+ 過去形 (条件), 仮定法過去 (would+ 動詞の原形) (結果) - 役割: 現在の事実とは異なること、あるいは実現の可能性が低いことを想定します。
- 例文:
Supposing you won the lottery, would you quit your job?（仮に宝くじに当たったとしたら、仕事を辞めますか？） - 注記: ここでの過去形は「過去の事」を表すのではなく、現実との「距離感（Distance）」を表しています。
- Type 3: 過去の反事実（Unreal Past）
- 構成:
Supposing+ 過去完了形 (条件), 仮定法過去完了 (would have+ 過去分詞) (結果) - 役割: 実際には起こらなかった過去の出来事を「もし起きていたら」と仮定して振り返ります。
- 例文:
Supposing they had invested in that startup ten years ago, they would have earned a fortune.（もし彼らが10年前にあのスタートアップに投資していたとしたら、巨万の富を得ていただろうに。）
- 名詞句や動名詞を伴う形（Participial Use）
- 構成:
Supposing+ 名詞句 / 動名詞句 - 役割:
in the event of（〜の場合には）に近い意味で、特定の事象を前提として置きます。 - 例文:
Supposing a sudden change in market trends, we must remain flexible.（市場トレンドの急激な変化を想定すると、我々は柔軟であり続けなければならない。）
that の有無Supposing that you agree... のように that を伴うこともありますが、現代英語（特に口語やビジネス文書）では省略されるのが一般的です。that を入れると、よりフォーマルで論理的な響きが強まります。supposing 節の時制 | メインの節の時制 | 日本語のニュアンス |will + 原形 | もし〜なら（あり得る） |would + 原形 | 仮に〜だとしたら（実際は違うが） |would have + 過去分詞 | もし〜だったとしたら（実際は違ったが） |supposing をいつ使うべきかを知ることは、C1レベルの表現力を身につける上で不可欠です。単に if を置き換えるのではなく、以下のような特定の文脈でその真価を発揮します。- 1困難な状況や、起こりにくいシナリオを検討する時
Supposing the funding is cut, how will the project proceed?（仮に資金援助が打ち切られたとしたら、プロジェクトはどう進めるつもりですか？）- この場合、
ifよりも「その事態を真剣にシミュレーションしよう」という強いメッセージが込められます。
- 1戦略的なプランニングやブレインストーミング
Supposing we expanded into the Southeast Asian market, what logistics challenges would we face?（東南アジア市場に進出すると仮定した場合、どのような物流上の課題に直面するでしょうか？）- 「仮説」を立てて議論をリードする上級者らしい表現です。
- 1フォーマルな議論や説得力のある論証
Supposing that the theory of relativity holds true in this context, the results are consistent.（相対性理論がこの文脈でも成立すると仮定すれば、結果は一貫していると言える。）
- 1相手に深い内省や想像を促す問いかけ
Supposing you could live anywhere in the world, where would you choose?（もし世界のどこにでも住めるとしたら、どこを選びますか？）ifを使うよりも、より「夢のような話」や「思考の遊び」としてのニュアンスが強まります。
- 1「もし〜だとしたらどうする？」という直接的な問い
Supposing he says no?（もし彼がノーと言ったらどうする？）- これは
What if he says no?とほぼ同じですが、supposingを使う方がやや落ち着いた、分析的な響きになります。
supposing を使う際に犯しやすいミスには、日本語の文法構造からの干渉（L1 Transfer）が大きく関わっています。- 1時制の一致のミス (Tense Mismatch)
- 間違い:
Supposing you win the lottery, what would you do?(現在形とwouldの混在) - 正解:
Supposing you won the lottery, what would you do?(非現実な仮定なので過去形を使用) - 理由: 日本語の「当たったら」という感覚につられて現在形（win）を使いがちですが、現在の事実と異なる仮定をする場合は、必ず時制を一つ戻す必要があります。
- 1単純な「事実」や「習慣」に対して使ってしまう
supposing は「仮定・想定」のニュアンスが強いため、単なる日常の習慣や確実な予定には不向きです。- 不自然:
Supposing it rains, I take the bus. - 正解:
If it rains, I take the bus.またはWhen it rains, I take the bus. - 理由:
supposingは「思考実験」を誘う言葉なので、単なる条件分岐（雨ならバス）に使うと大げさすぎて不自然に聞こえます。
- 1命令形の
Supposeとの混同
Suppose（動詞の命令形）と Supposing（接続詞的）は似ていますが、使い方が異なります。- 間違い:
Supposing that is true.(文として完結していない) - 正解:
Suppose that is true.(「それが本当だと考えてみて」という命令文) - 理由:
Supposingはあくまで従属節を作るものなので、後ろに主節（帰結節）が必要です。一方、Supposeはそれ単体で「〜だと仮定してみなさい」という命令文として成立します。
- 1助動詞の過剰使用
would を入れてしまうミスです。- 間違い:
Supposing you would have more time, what would you learn? - 正解:
Supposing you had more time, what would you learn? - 理由: 日本語の「〜だろうという状況なら」という思考が
wouldを誘発しますが、英語の条件節内では、原則としてwouldは使いません（時制で表現します）。
supposing と似た意味を持つ他の表現との違いを整理しましょう。これらを使い分けることで、表現の精度が飛躍的に高まります。if | 最も一般的でニュートラル。単純な条件。 | あらゆる場面 |supposing | 相手に「想定」を促す。思考実験的。 | 戦略会議、深い議論、仮説提示 |provided (that) | 「〜という条件でのみ」という強い限定。 | 契約書、公的な約束、許可 |as long as | 「〜である限りは」。期間や状態の継続。 | 条件の維持、日常的な約束 |what if | 「もし〜だったら？」という問いかけ。 | カジュアルな提案、不安の吐露 |assuming (that) | 「〜ということを当然の前提として」。 | 論理的な推論、計算、分析 |supposing vs provided (that)provided (that) は「もし〜という条件が満たされるなら（許可する、同意する）」という、非常に限定的な条件を指します。一方、supposing は「もし〜という状況が起きたら（どうなるか考えよう）」という、結果の探求に重点があります。I will go, provided you pay.(あなたが払うなら行くよ。＝条件)Supposing I pay, will you definitely come?(仮に私が払うとしたら、君は絶対に来るかい？＝想定の確認)
supposing vs assumingassuming は、すでにある程度の根拠があることや、議論を進めるために一旦置いておく前提に使われます。supposing よりも「事実である可能性が高い」または「論理的な出発点」というニュアンスが強いです。Assuming everyone is here, let's start.(全員揃っているという前提で、始めましょう。)
supposing は文頭でしか使えませんか？- 例:
What would you do supposing you lost your passport?（パスポートを失くしたと想定したら、どうしますか？）
suppose と supposing は完全に入れ替え可能ですか？Suppose は命令形として文を始め、その後に (that) + 節 が続きます。Supposing は分詞構文由来の接続詞として機能します。口語では Suppose you won... と Supposing you won... はほぼ同様に使われますが、Suppose の方がより直接的な問いかけに聞こえます。if よりも洗練された、論理的な印象を与えます。特にリスク管理や将来の予測について述べる際には非常に適切な表現です。ただし、非常にカジュアルな同僚とのやり取りであれば、if や what if の方が自然な場合もあります。supposing 節の中で were to を使うことはできますか？Supposing you were to fail... のように were to を使うと、「万が一〜ということがあれば」という、さらに起こる可能性が低い、あるいは起きてほしくないというニュアンスを強調できます。これは Type 2（仮定法過去）の強調形として非常に高度な表現です。Tense Usage with 'Supposing'
| Time Frame | Verb Form in Clause | Meaning | Example |
|---|---|---|---|
|
Present/Future (Likely)
|
Present Simple
|
Real possibility
|
Supposing it rains...
|
|
Present/Future (Unlikely)
|
Past Simple
|
Hypothetical/Dream
|
Supposing I won...
|
|
Present/Future (Formal)
|
Were to + Verb
|
Very unlikely/Formal
|
Supposing he were to die...
|
|
Past (Impossible)
|
Past Perfect
|
Counterfactual past
|
Supposing we had met...
|
Variations of the Conjunction
| Full Form | Shortened Form | Usage Note |
|---|---|---|
|
Supposing that...
|
Supposing...
|
The 'that' is usually omitted in speech.
|
|
Suppose that...
|
Suppose...
|
Identical in meaning to 'Supposing'.
|
|
Just supposing...
|
Supposing...
|
Adding 'just' makes it more speculative.
|
Meanings
A conjunction used to introduce a hypothetical condition or a 'what if' scenario, often used to prompt a discussion about consequences.
Speculative Future
Imagining a possible but unlikely future event.
“Supposing they offer you the job, will you take it?”
“Supposing we miss the train, is there a bus?”
Counterfactual Past
Imagining how the past could have been different.
“Supposing you hadn't intervened, what would have happened?”
“Supposing we had never met, where would you be now?”
Challenging an Assumption
Using a hypothesis to question someone's logic or plan.
“Supposing your theory is wrong; what's your Plan B?”
“Supposing he doesn't show up, do we start without him?”
Reference Table
| 条件の種類 | Supposing節 | 主節 | 例文 |
|---|---|---|---|
|
起こりうる未来（タイプ1）
|
Supposing + 現在形
|
未来形
|
Supposing you get the job, will you move?
|
|
非現実の現在/未来（タイプ2）
|
Supposing + 過去形
|
条件形（would + 動詞の原形）
|
Supposing you lived abroad, where would you go?
|
|
非現実の過去（タイプ3）
|
Supposing + 過去完了形
|
条件完了形（would have + 過去分詞）
|
Supposing I had known, I would have told you.
|
|
仮説（一般的）
|
Supposing + 名詞句
|
関連する節
|
Supposing a delay, we'll wait.
|
|
暗黙の疑問
|
Supposing + 節
|
疑問文
|
Supposing it rains, what then?
|
|
より丁寧なトーン
|
Supposing + 節
|
任意の条件形
|
Supposing the data is accurate, our conclusion stands.
|
フォーマル度スペクトル
Supposing one were to face redundancy, what measures would be taken? (Career discussion)
Supposing you lost your job, what would you do? (Career discussion)
Supposing you got fired, then what? (Career discussion)
Supposing you got the boot, how you gonna pay rent? (Career discussion)
レベル別の例文
Supposing it is cold?
What if it is cold?
Supposing you are late?
What if you are late?
Supposing we go now?
What if we go now?
Supposing he says no?
What if he says no?
Supposing you lose your phone?
What if you lose your phone?
Supposing the shop is closed?
What if the shop is closed?
Supposing they don't like the food?
What if they don't like the food?
Supposing we take a taxi?
What if we take a taxi?
Supposing you won the lottery, what would you buy?
If you won the lottery, what would you buy?
Supposing it rained all day, would we still go?
If it rained all day, would we still go?
Supposing you had a superpower, which one would it be?
If you had a superpower, which one would it be?
Supposing she forgot your birthday, would you be mad?
If she forgot your birthday, would you be mad?
Supposing the flight was canceled, how would we get home?
If the flight was canceled, how would we get home?
Supposing you hadn't studied, do you think you'd have passed?
If you hadn't studied, do you think you'd have passed?
Supposing we invested now, what are the risks?
If we invested now, what are the risks?
Supposing he doesn't agree to the terms, what's our next move?
If he doesn't agree to the terms, what's our next move?
Supposing the government were to collapse, what would follow?
If the government were to collapse, what would follow?
Supposing you had been born in a different century?
Imagine if you had been born in a different century?
Supposing we were to pivot our entire strategy this late in the game?
What if we changed our whole strategy now?
Supposing the evidence had been tampered with, the whole case would fall apart.
If the evidence had been tampered with, the case would fail.
Supposing, for the sake of argument, that his premise is entirely flawed.
Let's assume his idea is wrong for a moment.
Supposing we should find ourselves in a position of absolute power?
What if we found ourselves with total power?
Supposing the very fabric of reality were to unravel before our eyes?
What if reality itself fell apart?
Supposing he had but one chance to redeem himself, would he take it?
If he had only one chance to save himself, would he?
間違えやすい
Learners confuse the hypothetical conjunction with the verb meaning 'expected to'.
Learners use 'Supposing if' together.
よくある間違い
Supposing you will go?
Supposing you go?
Supposing it is rain?
Supposing it rains?
Supposing you are rich, what would you do?
Supposing you were rich, what would you do?
Supposing you didn't meet him last year?
Supposing you hadn't met him last year?
文型パターン
Supposing ___ (Subject) ___ (Past Verb), what would happen?
Supposing ___ (Subject) hadn't ___ (Past Participle)...
Real World Usage
Supposing a conflict arose between team members, how would you mediate?
Supposing we just skip the party and watch a movie?
Supposing the interest rates rise next year, can we afford the mortgage?
Supposing you could only eat one food for the rest of your life, what is it?
Supposing the witness is lying, where does that leave your case?
Supposing the hotel is overbooked, do we have a backup?
仮定法のバリエーションを増やそう
if ばかり使っていませんか？「supposing」を使うと、あなたの英語がもっと「sophisticated」に、そして「complex」な仮説のシナリオを自在に操れるプロのように聞こえますよ。会話も「natural」で「engaging」になります。 "Supposing you try this, you'll see the difference."時制に気をつけよう
if の仮定法と同じように、「supposing」の節と主節の時制を合わせることがとっても大切です。非現実的な過去の話なら過去完了形、非現実的な現在や未来の話なら過去形を使います。これを間違えると「confusion」を招いてしまいますよ！ Supposing I had known, I would have told you.
ブレインストーミングで活用しよう
Supposing we doubled our efforts, what would be the outcome?
思慮深い印象を与えよう
Supposing we consider this from another angle, what might we find?
Smart Tips
Start your sentence with 'Supposing' to force your opponent to imagine your perspective.
Think about whether the event is possible. If it's just a dream, go one step back in time (Present -> Past).
Use 'Supposing that' to add a layer of professional distance and politeness.
Use 'Supposing' to turn a command into a suggestion.
発音
Stress on the second syllable
The word 'supposing' is stressed on the 'po'.
Rising intonation
Supposing it fails? ↗
Conveys uncertainty and invites the listener to provide a solution.
暗記しよう
記憶術
Supposing starts a Story: Imagine the Scenario.
視覚的連想
Imagine a person holding a crystal ball. Inside the ball is a tiny world where everything is different. 'Supposing' is the magic word that lets you look inside that ball.
Rhyme
When you want to guess and play, 'Supposing' is the word to say!
Story
A detective is at a crime scene. He says, 'Supposing the killer left through the window?' He isn't sure, but he is inviting his partner to imagine that specific path to see if it makes sense.
Word Web
チャレンジ
Write down three 'Supposing' questions about your life if you lived on Mars. Use the Past Simple.
文化メモ
British speakers often use 'Suppose' and 'Supposing' interchangeably in casual conversation to sound less direct.
Americans frequently use 'What if' in place of 'Supposing' in all but the most formal contexts.
In Western academia, 'Supposing' is a standard way to introduce a 'thought experiment' or a 'counter-argument'.
From the Old French 'supposer', meaning 'to put under' or 'to assume'.
会話のきっかけ
Supposing you could live anywhere in the world, where would you go?
Supposing you had been born 100 years ago, how would your life be different?
日記のテーマ
よくある間違い
Test Yourself
Supposing she ___ (know) about the surprise, she wouldn't have looked so shocked.
Find and fix the mistake:
Supposing he miss the bus, what he will do then?
Choose the correct sentence:
Score: /3
練習問題
8 exercisesSupposing you ___ (see) a ghost, what would you do?
Supposing we ___ (not/meet) that day, we wouldn't be married now.
Find and fix the mistake:
Supposing if you win the prize, how will you spend it?
[you / supposing / lost / passport / your / ?]
1. Supposing it rains... 2. Supposing you were rich... 3. Supposing you'd been late...
If you were the president, what would you change?
'Supposing' can be used to talk about things that actually happened in the past.
A: I'm worried about the presentation. B: ___, what's the worst that could happen?
Score: /8
Practice Bank
12 exercisesSupposing you ___ (see) your favorite celebrity, what would you say?
Supposing the flight ___ (be) delayed, how will we get to the meeting on time?
Supposing I had studied harder, I would pass the exam.
What would you do, supposing you will lose your wallet?
Choose the correct sentence:
Choose the correct sentence:
Translate into English: 'What if she didn't come? What would we do then?'
Translate into English: 'Imagine you lose your keys, where would you check first?'
Arrange these words into a sentence:
Arrange these words into a sentence:
Match the beginning of the sentence with the correct ending:
Match the 'supposing' clause with its appropriate main clause:
Score: /12
よくある質問 (8)
Yes, they are interchangeable. `Suppose we go?` and `Supposing we go?` mean the same thing, though `Supposing` is slightly more common as a conjunction.
It is neutral. It works in a business meeting (`Supposing we increase the budget?`) and in a casual chat (`Supposing we get pizza?`).
Not always, but it's very common because you are usually asking someone to imagine something. You can also use it in a statement: `Supposing it rains, we will stay home.`
This is called the 'subjunctive' or 'hypothetical' past. It shows that the situation is not real. `Supposing I won` means I haven't won yet.
No. This is a common mistake. Use one or the other: `If it rains...` or `Supposing it rains...`.
`Assuming` implies you think it's likely true. `Supposing` is just for imagination and doesn't care if it's likely or not.
Yes, but you must use the Past Perfect: `Supposing you had told me?` (But you didn't).
Yes, to set up a premise for an argument. `Supposing the hypothesis were true, we would expect...`
Scaffolded Practice
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Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
Suponiendo que
Spanish requires the subjunctive; English uses the indicative past.
En supposant que
English 'Supposing' is more common in casual speech than the French equivalent.
Angenommen
German uses a participle, while English uses a gerund/conjunction.
もしも (Moshimo)
Japanese is a particle/adverb, while 'Supposing' is a conjunction.
بفرض أن (Bifardi anna)
Arabic is much more formal and less common in daily texting/chatting.
假如 (Jiǎrú)
Chinese doesn't have tense backshifting, so the context must provide the time.
Learning Path
Prerequisites
Learn These First
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