英検1級のonly if・unless・even ifの違い｜必要条件と例外を読む独自40問【全解答】

結論：英検1級の内容一致で見落としやすいのが、ifとonly ifの必要条件・十分条件の違い、unlessの例外、even ifとeven thoughの仮定・事実の違いです。慶英会では、短文32問と独自英文2篇の8問を合わせたオリジナル40問と全解答を用意しました。長文・英文要約・意見論述・二次面接で、元の英文より主張を強めすぎない練習ができます。

英検1級の現行形式では短文の語句空所補充22問、長文空所補充6問、長文内容一致7問が出題されます。英検協会の公式形式もご覧ください。本文・設問は慶英会独自の創作であり、英検協会の過去問を転載していません。

先に理解する7つの条件表現

英文	基本的な論理	間違えやすいこと
If A, B.	AならB（AはBの十分条件）	BならAと逆転する
A only if B.	AならB（BはAに必要）	BだけでAが実現すると考える
B unless A.	AでなければBという規則	Aが成立した場合の結果まで断定する
Even if A, B.	Aが仮に起きてもB	Aが確定した事実と読む
Even though A, B.	実際にAだがB	仮定のifと混同する
B provided that A.	Aという条件のもとでB	条件なしでもBと考える
B as long as A.	Aの間・条件でB	期間と成立条件の関連を見失う

例：「The policy can be adopted only if an independent review is completed.」では独立審査の終了が採用の必要条件です。審査が終わっただけで採用が保証されるとは書かれていません。英検1級の選択肢がこの意味を逆転させていないか確認してください。

必要条件と十分条件の診断｜慶英会独自40問

if・only if：必要条件と十分条件

独自Q1

A certificate is awarded only if the candidate passes the assessment.

• (A) Passing is required for the award.
• (B) Passing guarantees an award.
• (C) All candidates are certified.
• (D) The assessment is optional.

独自Q2

If the alarm detects smoke, it activates a warning.

• (A) Warning requires smoke and no other cause.
• (B) Smoke detection is sufficient under the stated rule.
• (C) No other alerts exist.
• (D) The detector is always active.

独自Q3

Construction may start only if a permit is issued.

• (A) A permit makes all construction mandatory.
• (B) Construction is already finished.
• (C) A permit is necessary, but may not be sufficient.
• (D) No permit can be issued.

独自Q4

If supervisors agree, the review can begin.

• (A) Review is impossible without their agreement.
• (B) All supervisors agree.
• (C) The review has begun.
• (D) Their agreement is one sufficient route, not necessarily the only route.

独自Q5

A subsidy is available only if invoices are submitted.

• (A) Invoices are required under this policy.
• (B) Any invoice guarantees the subsidy.
• (C) Invoices are unnecessary.
• (D) Every firm receives the subsidy.

独自Q6

If additional funds arrive, the laboratory can expand.

• (A) Expansion already occurred.
• (B) Funding would enable expansion under the stated condition.
• (C) Expansion is impossible by any other means.
• (D) Funds are certain to arrive.

独自Q7

The project can continue only if reviewers approve its safety plan.

• (A) Approval is irrelevant.
• (B) The project has already continued.
• (C) Reviewers’ approval is necessary for continuation.
• (D) All plans are always approved.

独自Q8

If the report is complete, it will be published.

• (A) The report is already online.
• (B) Completion is impossible.
• (C) No report can ever be published.
• (D) The statement does not prove publication can happen only after completion.

unless・otherwise：例外と否定

独自Q9

Unless heavy rain starts, the festival will proceed.

• (A) Without heavy rain, the festival proceeds under the stated rule.
• (B) Heavy rain must start.
• (C) The festival is permanently cancelled.
• (D) All rain prevents every event.

独自Q10

A permit remains valid unless the owner cancels it.

• (A) Cancellation is impossible.
• (B) Without cancellation, validity continues under the rule.
• (C) The permit is already cancelled.
• (D) A permit lasts forever regardless of events.

独自Q11

Unless the network fails, the alert is delivered.

• (A) All alerts are guaranteed under every condition.
• (B) The network must fail.
• (C) The sentence does not establish that failure prevents every possible alternative delivery.
• (D) The system has no network.

独自Q12

Submit the form by Friday; otherwise, the review may be delayed.

• (A) Otherwise means if the form is submitted.
• (B) The review was completed.
• (C) No deadlines exist.
• (D) Otherwise means failure to submit by Friday.

独自Q13

The library stays open unless a safety inspection requires closure.

• (A) The specified closure requirement is an exception to opening.
• (B) No inspections occur.
• (C) The library can never close.
• (D) The library must close today.

独自Q14

Unless fees decrease, fewer customers may register.

• (A) Registration is certainly zero.
• (B) Without fee reductions, fewer registrations are possible rather than certain.
• (C) Fees have already fallen.
• (D) Every customer must register.

独自Q15

The study continues unless the ethics board finds a serious issue.

• (A) No ethical problem ever occurs.
• (B) All studies everywhere end.
• (C) The rule does not imply every minor concern forces all research to stop.
• (D) Researchers never need review.

独自Q16

The launch will be postponed unless essential tests pass.

• (A) Every test passed.
• (B) The launch is permanently cancelled.
• (C) Testing is irrelevant.
• (D) Failure to pass the essential tests triggers postponement.

even if・even though：仮定と事実

独自Q17

Even if predictions improve, residents need clear messages.

• (A) The need remains under a hypothetical improvement.
• (B) Predictions have certainly improved.
• (C) No communication is required.
• (D) The forecast has been cancelled.

独自Q18

Even though the forecast improved, the response plan remained weak.

• (A) Improvement is purely hypothetical.
• (B) The forecast is described as having improved.
• (C) No forecast exists.
• (D) The plan was certainly effective.

独自Q19

Even if an application is free, access may remain unequal.

• (A) The fee certainly exists.
• (B) Every person is excluded.
• (C) Removing the fee alone may not eliminate other barriers.
• (D) Access is always equal.

独自Q20

Even though enrollment increased, learning was not measured.

• (A) Everyone improved.
• (B) No one enrolled.
• (C) Enrollment is impossible.
• (D) Learning improvement is not proven by enrollment counts.

独自Q21

Even if storage is added, the power system may require other measures.

• (A) Storage alone is not guaranteed to solve every need.
• (B) Storage is already installed.
• (C) Storage is always useless.
• (D) All energy comes from storage.

独自Q22

Even though the project met its output target, outcomes remained uncertain.

• (A) No target was met.
• (B) The specified output target was achieved.
• (C) All outcomes were measured.
• (D) The programme failed every target.

独自Q23

Even if research methods are public, personal data may stay protected.

• (A) All personal records are automatically released.
• (B) Transparency is impossible.
• (C) Open methods can coexist with protected records.
• (D) Personal data must be sold.

独自Q24

Even though warnings were issued, some households missed them.

• (A) No warnings were issued.
• (B) Every household received one.
• (C) The message was understood everywhere.
• (D) The text contradicts the claim of universal receipt.

provided that・as long as：実施条件

独自Q25

The trial may proceed provided that records are protected.

• (A) Protection is a stated condition.
• (B) All records become public.
• (C) The trial has been completed.
• (D) No condition exists.

独自Q26

The course is funded as long as qualified teachers are available.

• (A) Teachers are optional.
• (B) Availability of qualified teachers is a condition of funding.
• (C) Funding has ended.
• (D) Every teacher is qualified.

独自Q27

Access is granted provided that identity checks succeed.

• (A) Identity checks are unnecessary.
• (B) All access requests must be rejected.
• (C) Successful checks are required.
• (D) Any user may bypass the rules.

独自Q28

The route remains open as long as travel is safe.

• (A) All travel is always safe.
• (B) The route is permanently closed.
• (C) Weather is irrelevant.
• (D) The duration of opening is tied to safe conditions.

独自Q29

The firm shares selected data provided that the board agrees.

• (A) Board approval is a stated prerequisite.
• (B) All records must be shared.
• (C) No board exists.
• (D) The board has definitely agreed.

独自Q30

Users can continue as long as their subscription is active.

• (A) Subscriptions cannot expire.
• (B) An active subscription is the relevant continuing condition.
• (C) The service is free forever.
• (D) No users are allowed.

独自Q31

The project may expand provided that the trial meets safeguards.

• (A) Every trial expands automatically.
• (B) The safeguards have been abandoned.
• (C) Safeguards matter, but expansion is still expressed as a possibility.
• (D) Expansion was completed yesterday.

独自Q32

Equipment may be borrowed for as long as the agreement remains valid.

• (A) The arrangement is unconditional.
• (B) The agreement must have expired.
• (C) Ownership permanently transfers.
• (D) Borrowing duration is tied to the valid agreement.

慶英会独自英文2篇｜条件・例外を読む8問

Passage 1：Flood-warning policy

A fictional city plans a flood-warning pilot. The city will authorize the system only if an independent security review has been completed. Completion of the review is not sufficient for authorization, because officials must also consider costs. The service will send digital warnings unless its network is unavailable. Even if the alerts are delivered, some residents may be unable to interpret them or respond. The city will run community training provided that agreed safety procedures are in place. It will review real outcomes rather than count notifications alone.

Passage 2：Research-data sharing

A fictional research group plans to release a transport study. Aggregated results may be shared if a committee verifies appropriate safeguards. Detailed personal records will be available only if additional authorization is granted. Public explanations will continue unless a justified correction requires temporary withdrawal. Even if one outside group reproduces one analysis, the researchers will not claim that every result is independently verified. Collaboration can continue as long as partners follow the agreed data-protection rules.

独自Q33〜36はPassage 1、Q37〜40はPassage 2の本文を根拠に答えてください。

独自Q33

City pilot: What is required for authorization?

• (A) Completion of an independent security review.
• (B) A public download count.
• (C) A permanent license.
• (D) An international treaty.

独自Q34

City pilot: Does completing that review guarantee authorization?

• (A) Yes, it is the only consideration.
• (B) No, cost is also considered.
• (C) The review was not completed.
• (D) Authorization is prohibited.

独自Q35

City pilot: What occurs unless its digital network becomes unavailable?

• (A) No warnings can ever be sent.
• (B) No one can understand the warning.
• (C) The service sends digital warnings under the stated rule.
• (D) The pilot is cancelled automatically.

独自Q36

City pilot: Why is alert delivery insufficient as a success metric?

• (A) All residents have the same needs.
• (B) No alerts are delivered.
• (C) The network is always down.
• (D) Some recipients may not understand or be able to respond.

独自Q37

Research group: When may aggregated results be shared?

• (A) When the committee verifies suitable safeguards.
• (B) When every personal record is released.
• (C) Whenever any visitor requests access.
• (D) Without any review.

独自Q38

Research group: What is required for detailed record access?

• (A) Only knowing the study title.
• (B) Additional authorization.
• (C) Only reading the abstract.
• (D) No permission of any kind.

独自Q39

Research group: When may an explanation be temporarily withdrawn?

• (A) When the website receives many visitors.
• (B) Whenever a researcher disagrees.
• (C) When a justified correction requires it.
• (D) Only after every grant is renewed.

独自Q40

Research group: What is not justified by reproducing one analysis?

• (A) The group tested one analysis.
• (B) One result has been checked.
• (C) Other analyses might need review.
• (D) Every result in the project has been independently verified.

40問の正解・条件の向き・誤答の根拠

if・only if：必要条件と十分条件

Q1 正解（A）Passing is required for the award.。only if は証書の授与→評価合格。必要条件であり十分条件とは限らない。

Q2 正解（B）Smoke detection is sufficient under the stated rule.。If A, B のAはBの十分条件。逆は未保証。

Q3 正解（C）A permit is necessary, but may not be sufficient.。only if は必要性で、許可だけで自動着工とはならない。

Q4 正解（D）Their agreement is one sufficient route, not necessarily the only route.。ifをonly ifへ勝手に変更しない。

Q5 正解（A）Invoices are required under this policy.。必要条件と十分条件を区別。

Q6 正解（B）Funding would enable expansion under the stated condition.。資金の到着は文中の一条件で、他の可能性は否定していない。

Q7 正解（C）Reviewers’ approval is necessary for continuation.。継続するなら承認されているという関係。

Q8 正解（D）The statement does not prove publication can happen only after completion.。ifとonly ifの違い。

unless・otherwise：例外と否定

Q9 正解（A）Without heavy rain, the festival proceeds under the stated rule.。unless rain＝if not rain。雨が降る場合の全結果は未確定。

Q10 正解（B）Without cancellation, validity continues under the rule.。unless節が例外。

Q11 正解（C）The sentence does not establish that failure prevents every possible alternative delivery.。network failureなら代替が絶対不可能とは述べていない。

Q12 正解（D）Otherwise means failure to submit by Friday.。otherwiseは条件が満たされない場合。

Q13 正解（A）The specified closure requirement is an exception to opening.。安全上の閉鎖要請がなければ開館という原則。

Q14 正解（B）Without fee reductions, fewer registrations are possible rather than certain.。mayという不確実性を保つ。

Q15 正解（C）The rule does not imply every minor concern forces all research to stop.。serious と当該研究の範囲を保つ。

Q16 正解（D）Failure to pass the essential tests triggers postponement.。unless passはif not pass。

even if・even though：仮定と事実

Q17 正解（A）The need remains under a hypothetical improvement.。even ifは仮定しても結論が変わらない。

Q18 正解（B）The forecast is described as having improved.。even thoughは既成事実の譲歩。

Q19 正解（C）Removing the fee alone may not eliminate other barriers.。価格以外の障壁。

Q20 正解（D）Learning improvement is not proven by enrollment counts.。活動量と成果の差。

Q21 正解（A）Storage alone is not guaranteed to solve every need.。even if＋mayの限定を維持する。

Q22 正解（B）The specified output target was achieved.。outputとoutcomeを区別。

Q23 正解（C）Open methods can coexist with protected records.。研究方法の公開と記録の全面公開は別。

Q24 正解（D）The text contradicts the claim of universal receipt.。allへ不当に一般化しない。

provided that・as long as：実施条件

Q25 正解（A）Protection is a stated condition.。provided thatは条件。

Q26 正解（B）Availability of qualified teachers is a condition of funding.。条件つきの継続。

Q27 正解（C）Successful checks are required.。provided thatによって条件が提示されている。

Q28 正解（D）The duration of opening is tied to safe conditions.。as long asの時間・条件の重なり。

Q29 正解（A）Board approval is a stated prerequisite.。selected data という範囲も残す。

Q30 正解（B）An active subscription is the relevant continuing condition.。契約状態が条件。

Q31 正解（C）Safeguards matter, but expansion is still expressed as a possibility.。may を必ず実施へ強めない。

Q32 正解（D）Borrowing duration is tied to the valid agreement.。期間の条件。

慶英会独自英文2篇｜条件・例外を読む8問

Q33 正解（A）Completion of an independent security review.。only if review completedは必要条件。

Q34 正解（B）No, cost is also considered.。安全評価だけでは費用等の条件を満たさない。

Q35 正解（C）The service sends digital warnings under the stated rule.。unless unavailable。

Q36 正解（D）Some recipients may not understand or be able to respond.。even if deliveredを読んで受信と行動を分ける。

Q37 正解（A）When the committee verifies suitable safeguards.。if review confirms protection。

Q38 正解（B）Additional authorization.。only if additional authorization。

Q39 正解（C）When a justified correction requires it.。unless justified correction。

Q40 正解（D）Every result in the project has been independently verified.。even if one analysis reproduced, not all.

英検1級の長文・要約・面接へ転用する4つの方法

• **Reading：**本文はAのみ必要条件を示すのに、選択肢でAだけで十分と断定していないか確認する。
• **英文要約：**only if、unless、may、even ifの条件が結論を左右するなら削らない。
• **意見論述：**政策の効果を保証せず、必要な費用・データ・実行条件を明示する。
• **二次面接：**Even if the policy offers benefits, it may impose additional costs.のように譲歩と制約を答える。

7日間の復習手順

• 1日目：ifとonly ifのQ1〜8で必要・十分を区別する。
• 2日目：unlessとotherwiseのQ9〜16で例外条件を整理。
• 3日目：even ifとeven thoughのQ17〜24で事実と仮定を区別。
• 4日目：provided thatとas long asのQ25〜32を初見演習。
• 5日目：Passage 1のQ33〜36で条件を追う。
• 6日目：Passage 2のQ37〜40で情報の範囲を正確に読む。
• 7日目：英検1級の公式過去問で条件節のある英文を探し、誤答を再検証。

FAQ

ifとonly ifは同じ意味ですか？

どちらも条件を表しますが、英文の主節と条件節の関係が異なります。A only if B はA→Bであり、BだけでAが保証されるわけではありません。

unless はif notと同じですか？

多くの条件文ではunless Aをif not Aと整理できますが、文脈に応じて意味を確認してください。例外が生じた場合のすべての結果が決まるわけではありません。

even ifとeven thoughはどちらも『たとえ』ですか？

even if は仮定的、even though は事実の譲歩が中心です。言い換えると本文の主張が変わる場合があります。

公式参考情報・関連教材

• 英検協会｜1級公式形式
• 2026年第2回の過去問・音源・解答と慶英会独自32問
• 長文内容一致7問と根拠つき全解説
• 英文要約90〜110語の修正20例
• 英検1級総合教材ガイド

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