A conditional sentence usually consists of a main clause and an ‘if’ clause, and it is used for talking about possible or imaginary situations.
The order of the two clauses is not important; it depends on the speaker’s intention which of the two comes first.
When the if clause is first, there is a comma (,) after it in writing.
First Conditional (conditional type 1, open condition)
Real and possible situation, it’s likely that the condition will be fulfilled.
Main clause: future with will + infinitive, if clause: present.
- We will stay at home if it rains. (Reference to the future.)
- The boss will get angry if I’m late for work. (Reference to the future.)
- They will finish early if the machine works well. (Reference to the future, the condition is open, it’s possible that they finish early.)
- If we get the money for this job, we’ll buy a new washing machine. (Future reference, open possibility and likelihood.)
- If you leave now, you’ll catch the last bus. (Present situation with present or future possibility.)
- Will you help my sister if she asks you? (Future reference.)
Second Conditional (conditional type 2, half-open condition)
Imaginary situation, unreal, hypothetical condition which might be fulfilled only in theory.
Main clause: would + infinitive, if clause: past.
In conditional sentences the past form of be is were in every person in formal language, but was is also often used in spoken English.
- We would stay at home if it rained. (Reference to present time.)
- The boss would get angry if I was/were late for work. (Reference to the present.)
- They would finish earlier if the machine worked well. (It doesn’t work well, so they won’t finish / aren’t finishing early.)
- If I were rich, I’d buy a house by the seaside. (Imaginary situation, reference to the present or future)
- If you left now, you’d catch the last bus. (Present situation with present or future possibility, for which the condition should be fulfilled.)
- Would you help my sister if she asked you? (Present hypothesis.)
Third Conditional (conditional type 3, closed condition)
Impossible condition which cannot be fulfilled as the action or event already took place in the past.
Main clause: would + perfect infinitive, if clause: past perfect.
- We would have stayed at home if it had rained. (Reference to the past – it didn’t rain and we didn’t stay at home.)
- The boss would have got angry if I had been late for work. (Reference to the past – I wasn’t late and he wasn’t angry.)
- They would have finished earlier if the machine hadn’t broken down. (It broke down, so they didn’t finish early.)
- If I had won the lottery, I would have bought a house by the sea. (Impossibility – I didn’t win and I couldn’t buy a house.)
- If you had left in time, you would have caught the last bus. (Past reference, now it’s late to do anything about it.)
Would you have helped my sister if she had asked you? (No possibility, she didn’t ask you.)
Certainty, factual implication, general fact, overall truth – the result of this condition is always the same.
Main clause: present, if clause: present.
- Water boils if you heat it to 100 degrees Celsius.
- It gets dark if the sun goes down.
- A green light comes up if you press the button.
- My boss gets angry if I’m late for work.
The time of the if clause is different from the time of the main clause, several kinds of combinations may be used.
- If you had taught me how to make muffins (then in the past), I wouldn’t have to buy them in a shop (now).
- I would buy a house by the sea (now or in the future) if I had won the lottery last week.
- If I were in my mother’s house, I wouldn’t have stayed up so late last night.
- We would have scored more in the match yesterday if we were good players.
If modal verbs like can/could, may/might or should are used in the main clause, they replace will:
- We can go to the seaside if you have time tomorrow.
- If you leave now, you may catch the last bus.
- They might have finished earlier if the machine hadn’t broken down.
- If you wanted to pass the exam, you should study much harder. (You would have to study much harder.)
Normally we don’t use will or would in if clauses, except when they express willingness, for example in requests (they have a modal meaning then):
- If you will phone the manager now, he will surely make an appointment with you. (willingness)
- I would be very thankful if you would help me with my homework. (very polite request)
Should in if clauses may mean ‘if perhaps, by any chance’:
- I would be very happy if he should turn up at the party. (He’s not at all likely to come, but perhaps…)
In negative sentences we can use unless instead of if … not:
- You won’t pass the exam unless you study very hard. (= if you don’t study very hard)
If can be omitted with inverted word order (usually in the third conditional if the if clause comes first, and also in the second if the verb is were):
- Were I rich, I would buy a house by the sea. (= if I were rich)
- Had your sister come earlier, I would have shown her round the house. (= if she had come earlier)
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