A conditional sentence has two parts: the if-clause (the condition) and the main clause (the result). The verb pattern in each part tells the listener how real the condition is.
Type 1 is real and possible: if it rains, we will stay home. Type 2 is imaginary or unlikely: if I had a boat, I would sail around the world. Type 3 is impossible, because the moment has passed: if I had studied, I would have passed.
The grammar looks like four separate rules, but it is one idea with three settings: how likely is the condition, and is it in the present or the past? This page shows each setting, the comma rule, and the mistakes that examiners see most often.
The rule
The shape of a conditional
- If-clause first: "If it rains, we will stay home." Use a comma between the two parts.
- Main clause first: "We will stay home if it rains." No comma before "if".
- The if-clause never takes will, would or had in the standard patterns. Will and would live in the main clause.
- Unless means if not: "Unless you hurry, we will miss the train."
Zero conditional: facts and habits
- Pattern: if + present simple, present simple.
- Use it for things that are always true or always happen.
- "If you heat water to 100 degrees, it boils."
- "If I drink coffee after six, I cannot sleep."
First conditional: a real future possibility
- Pattern: if + present simple, will + base verb.
- The condition is possible and the result is in the future.
- "If the bus arrives on time, we will catch the 9 o'clock train."
- Use can, may or going to in the main clause when they fit better: "If you finish early, you can go home."
Second conditional: imaginary present or future
- Pattern: if + past simple, would + base verb.
- The condition is not true now, or is very unlikely.
- "If I had more time, I would learn the piano." (I do not have more time.)
- With the verb be, use were for every person in careful English: "If I were you, I would apologise."
- The past form here does not mean past time. It creates distance from reality.
Third conditional: the impossible past
- Pattern: if + had + past participle, would have + past participle.
- We imagine a different past and its result. Both parts are past.
- "If she had left earlier, she would have caught the train." (She did not leave earlier, and she missed it.)
- Mixed conditionals exist: "If I had studied medicine, I would be a doctor now" (past condition, present result).
Examples
- If you freeze water, it becomes ice.Zero conditional: a scientific fact.
- If I finish work early, I will call you.First conditional: a real possibility.
- If I had a bigger garden, I would grow vegetables.Second conditional: my garden is small, so this is imaginary.
- If I were you, I would take the job.Were, not was, in careful English. This is advice.
- If they had booked earlier, they would have paid less.Third conditional: the booking is in the past and cannot change.
- We will miss the start if we do not leave now.Main clause first, so no comma.
- Unless you water it, the plant will die.Unless means if not.
- If you see her, can you tell her I called?Can in the main clause keeps the request friendly.
- If I had known about the traffic, I would have left home earlier.Both clauses are in the past. I did not know, and I did not leave early.
- If I had learned Spanish as a child, I would speak it fluently now.Mixed conditional: past condition, present result.
Common mistakes
- Wrong: If it will rain tomorrow, we will stay home. Right: If it rains tomorrow, we will stay home.
- The if-clause uses the present simple even when the meaning is future. Will belongs to the main clause.
- Wrong: If I would be rich, I would buy an island. Right: If I were rich, I would buy an island.
- The second conditional uses the past simple in the if-clause. Never put would there.
- Wrong: If I had known, I would tell you. Right: If I had known, I would have told you.
- When the if-clause looks at the past, the result clause needs would have plus the participle.
- Wrong: Unless you do not hurry, we will miss the train. Right: Unless you hurry, we will miss the train.
- Unless already carries the negative meaning. Adding "do not" creates a double negative.
- Wrong: If I will see him, I will tell him. Right: If I see him, I will tell him.
- A possible future condition takes the present simple in the if-clause.
Practice drill
Answer all 20 questions. Each answer is marked at once, and the rule is explained under the question.
If it ___ tomorrow, we will cancel the picnic.
Show answer and explanation
Answer: A. rains The first conditional uses the present simple in the if-clause: if it rains.
If I ___ you, I would apologise.
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Answer: B. were The second conditional uses were for every person in careful English: If I were you.
If she had taken the earlier train, she ___ on time.
Show answer and explanation
Answer: C. would have arrived Third conditional: if + had + participle, would have + participle.
If you heat ice, it ___.
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Answer: D. melts Zero conditional for a general fact: if + present, present.
I would travel more if I ___ more money.
Show answer and explanation
Answer: A. had Second conditional: the past simple "had" shows that reality is different. I do not have enough money.
We will be late ___ we leave now.
Show answer and explanation
Answer: B. unless Unless means if we do not. "We will be late unless we leave now" is the correct pattern.
If I had known about the meeting, I ___ my plans.
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Answer: C. would have changed The if-clause is in the past, so the result uses would have changed.
If you finish your homework early, you ___ watch a film.
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Answer: D. can Can fits a real present or future opportunity in a first conditional main clause.
Please call me if you ___ late.
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Answer: A. are A real future possibility takes the present simple in the if-clause: if you are late.
If I ___ the answer, I would tell you.
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Answer: B. knew Second conditional, imaginary present: if I knew. I do not know the answer.
She would have passed the exam if she ___.
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Answer: C. had studied Third conditional if-clause: if + had + past participle.
If I eat too much sugar, I ___ bad.
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Answer: D. feel Zero conditional for a personal habit: if + present, present.
If it ___ colder, it would snow.
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Answer: A. were The second conditional uses the past subjunctive were, even with "it". The present reality is that it is not cold enough.
Unless you ___ the form, we cannot process the application.
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Answer: B. sign Unless already means if you do not, so the verb stays positive: unless you sign.
If they had left at dawn, they ___ the storm.
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Answer: C. would have missed Third conditional result: would have plus the past participle, missed.
If I ___ his number, I would call him right now.
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Answer: D. had Imaginary present with a present result: if I had his number, I would call him. The past form "had" shows I do not have it.
You will burn the rice ___ you turn down the heat.
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Answer: A. unless Unless means if you do not. The sentence needs the negative meaning that unless provides.
If I ___ younger, I would study abroad.
Show answer and explanation
Answer: B. were Second conditional: were marks an unreal present. I am not younger now.
He said he would come if he ___ time.
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Answer: C. had After a past reporting verb, the second conditional shifts back: he would come if he had time.
If the weather ___ nice tomorrow, we will walk to the beach.
Show answer and explanation
Answer: D. is First conditional with a real future possibility: if the weather is nice.
Questions learners ask
How many types of conditional are there?
Coursebooks teach four main types: zero (facts), first (real future), second (imaginary) and third (impossible past). Real English also mixes them, as in "If I had studied medicine, I would be a doctor now". Learn the four patterns first, then treat mixed conditionals as a bonus.
Should I write "if I was" or "if I were"?
Both appear. "If I were" is the careful form and it is standard in writing and exams. In casual speech many native speakers say "if I was". Use "were" in the second conditional, and keep "was" for a real past situation: "If I was late, my father drove me to school."
Can "will" ever appear in an if-clause?
Yes, in three cases. First, when "if" means "whether": "I do not know if it will rain." Second, when "will" means willingness: "If you will wait a moment, I will call him." Third, when it means a polite request: "If you will sign here, please." None of these is a standard first conditional.
More grammar topics
First conditional
If plus the present simple, will plus the base verb: a real possibility in the future.
Second conditional
If plus the past simple, would plus the base verb: the present that is not real.
Third conditional
If plus had and the past participle, would have plus the past participle: the past that cannot change.
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