英語の条件文：完全文法ガイド

ゼロ・第一条件文

"If + present simple, present simple"

Zero conditional: expresses universal truths, scientific facts, and general habits that are always true

"If you heat water to 100°C, it boils."

ゼロ・第一条件文

"If + present simple, will + base verb"

First conditional: expresses real, likely future conditions and their probable results

"If she studies every day, she will pass the exam."

ゼロ・第一条件文

"When vs. If (zero conditional)"

"When" implies certainty that the condition will occur; "if" implies it might or might not happen

"When I get home, I make tea. / If I get home early, I might make tea."

ゼロ・第一条件文

"Unless + positive verb"

Means "if … not" — introduces a negative condition with zero or first conditional structure

"Unless you book in advance, you won't get a seat."

ゼロ・第一条件文

"As long as / provided that"

Conditional conjunctions meaning "on the condition that" — often interchangeable with "if" in first conditional

"I'll help you as long as you promise to practise afterwards."

ゼロ・第一条件文

"Shall / can / may instead of will"

Modal verbs other than "will" can appear in the main clause of a first conditional to express ability, permission, or obligation

"If you finish early, you can leave."

ゼロ・第一条件文

"If + present continuous"

Zero/first conditional can use present continuous in the "if" clause to describe ongoing actions as conditions

"If you're feeling tired, you should rest."

ゼロ・第一条件文

"Imperative in the main clause"

First conditional can use an imperative instead of "will" to give instructions or advice based on a condition

"If the light turns green, press the button immediately."

第二条件文

"If + past simple, would + base verb"

Core second conditional structure for unreal or hypothetical present/future situations

"If I had more time, I would learn Japanese."

第二条件文

"Were instead of was"

In formal English, "were" is used for all persons in the second conditional "if" clause — even "I" and "he/she"

"If I were you, I would apply for that job."

第二条件文

"Could / might instead of would"

Replace "would" with "could" (ability) or "might" (possibility) to add nuance to the hypothetical outcome

"If she practised more, she could win the competition."

第二条件文

"Wish + past simple"

"Wish" followed by past simple expresses regret or desire to change a present situation — functionally related to second conditional

"I wish I spoke French fluently."

第二条件文

"If only + past simple"

A stronger, more emphatic version of "wish" for expressing dissatisfaction with a current situation

"If only I knew the answer right now!"

第二条件文

"Would rather + past simple"

Expresses a hypothetical preference about what someone else does — uses past simple after "would rather"

"I would rather she stayed here tonight."

第二条件文

"It's time + past simple"

Expresses that something should happen now — similar to second conditional in meaning but with a fixed structure

"It's time you started thinking about your future."

第二条件文

"Supposing / imagine + past simple"

Discourse markers that introduce second conditional hypotheticals — common in spoken English

"Supposing you had a million pounds, what would you do?"

第三条件文

"If + past perfect, would have + past participle"

Core third conditional structure for imagining how the past could have been different

"If you had called me, I would have helped you."

第三条件文

"Could have / might have in main clause"

Replace "would have" to express hypothetical past ability (could have) or possibility (might have)

"If we had left earlier, we might have caught the train."

第三条件文

"Wish + past perfect"

Expresses regret about a past action or situation that can no longer be changed

"I wish I had taken that job offer."

第三条件文

"If only + past perfect"

An emphatic form of regret about a past situation — stronger emotion than "I wish"

"If only I had listened to my teacher's advice!"

第三条件文

"Should have + past participle"

Expresses criticism or regret about a past action — can appear in main clause instead of "would have"

"If you had told me the truth, I would have helped; you should have been honest."

第三条件文

"Had + subject + past participle (inverted)"

Formal inversion of third conditional — removes "if" and inverts subject and auxiliary "had"

"Had I known about the delay, I would have taken a different route."

第三条件文

"If it hadn't been for"

Fixed third conditional phrase attributing an outcome to a specific cause or person

"If it hadn't been for her encouragement, I would never have finished the book."

第三条件文

"But for + noun phrase"

Formal equivalent of "if it hadn't been for" — common in written English and legal language

"But for the timely warning, the accident could have been catastrophic."

混合条件文

"If + past perfect, would + base verb (past → present)"

Mixed conditional type 1: an unreal past condition leads to a hypothetical present result

"If I had studied medicine, I would be a doctor now."

混合条件文

"If + past simple, would have + past participle (present → past)"

Mixed conditional type 2: a present unreal state implies a different past outcome

"If I were more organised, I would have finished this project weeks ago."

混合条件文

"If + past perfect, could + base verb"

Mixed conditional with modal "could" — a past event limits or enables a present ability

"If you had taken the course, you could apply for that position today."

混合条件文

"If + past simple, might have + past participle"

Mixed conditional expressing how a current trait or state may have influenced a past event

"If she were less stubborn, she might have accepted the compromise."

混合条件文

"Identifying time markers in mixed conditionals"

"Now", "today", "still", "already" in the main clause signal a mixed conditional — check both clauses for their time reference

"If he had invested wisely, he would still be working in finance now."

混合条件文

"Always / never as time-neutral modifiers"

"Always" or "never" in the main clause often signals a mixed conditional about permanent states or character

"If I had been born in France, I would always speak French at home."

混合条件文

"Would be doing (continuous) in mixed conditionals"

The main clause can use "would be + -ing" to emphasise an ongoing present or future activity

"If she had accepted the scholarship, she would be studying in Boston right now."

混合条件文

"Could have vs. would have in mixed context"

"Could have" in main clause = hypothetical ability in the past; "would have" = definite hypothetical action — choose based on meaning

"If I spoke Spanish, I could have translated the document yesterday."

倒置・フォーマル条件文

"Should + subject + base verb"

Formal inversion of first conditional — removes "if" and fronts "should"; implies slight doubt about the condition

"Should you require further assistance, please contact our support team."

倒置・フォーマル条件文

"Were + subject + to + base verb"

Formal inversion of second conditional — highly formal, common in contracts and official writing

"Were the committee to approve the proposal, funding would be released immediately."

倒置・フォーマル条件文

"Had + subject + past participle"

Formal inversion of third conditional — very common in academic, legal, and literary contexts

"Had the pilot not reacted quickly, the consequences could have been fatal."

倒置・フォーマル条件文

"Were it not for"

Formal inverted phrase equivalent to "if it were not for" — used for present or future hypotheticals

"Were it not for modern antibiotics, many routine infections would be fatal."

倒置・フォーマル条件文

"Were it not for vs. Had it not been for"

"Were it not for" = present/future hypothetical; "Had it not been for" = past hypothetical — do not confuse the two

"Had it not been for her donation, the charity would have closed last year."

倒置・フォーマル条件文

"Only if (fronted conditional)"

Fronting "only if" causes subject-auxiliary inversion in the main clause — highly formal and emphatic

"Only if all members agree will the resolution be passed."

倒置・フォーマル条件文

"Not unless (fronted negative)"

Fronting "not unless" also triggers inversion in the main clause — used for strong restrictions

"Not unless the contract is signed will we proceed with delivery."

倒置・フォーマル条件文

"On condition that / in the event that"

Formal conditional conjunctions used in legal, business, and academic writing instead of "if"

"The loan will be granted on condition that the borrower provides adequate collateral."

上級・特殊条件文

"If + were to + base verb (remote future)"

Expresses a hypothetical future event that is considered very unlikely or purely theoretical

"If the sun were to disappear, Earth would freeze within a week."

上級・特殊条件文

"Implied conditional (without "if")"

A conditional meaning can be conveyed without "if" using context — common with imperatives and conjunctions

"Study hard and you will succeed. (= If you study hard, you will succeed.)"

上級・特殊条件文

"Otherwise / or else as conditional connectors"

"Otherwise" and "or else" introduce the negative consequence of a preceding condition or instruction

"You need to leave now; otherwise, you'll miss the last train."

上級・特殊条件文

"Even if vs. Even though"

"Even if" introduces a hypothetical concessive condition; "even though" refers to a known, real concession

"Even if it rains tomorrow, we'll hold the event outside."

上級・特殊条件文

"Whether or not"

Expresses that the result is the same regardless of the condition — both possibilities are covered

"Whether or not you apologise, the damage has been done."

上級・特殊条件文

"If so / if not (elliptical conditionals)"

Short forms referring back to a previously mentioned condition — "if so" = if that is true; "if not" = if that is not true

"Are you free on Friday? If so, let's meet for coffee."

上級・特殊条件文

"Conditional perfect continuous (would have been + -ing)"

Describes what would have been happening at a past moment if a condition had been met — emphasises ongoing action

"If the project had started on time, we would have been finishing it this week."

上級・特殊条件文

"Subjunctive in conditionals"

The subjunctive mood (bare infinitive after "that" or "were") appears in formal conditionals and "wish" structures

"It is essential that every student be given a fair opportunity to retake the exam."