In English there are four basic conditional structures, although these can be mixed according to the situation. (They can also be mixed in other languages).
The tenses I’ve used are the basic tenses. However, once you know the general structures you can check what other verb forms you can use.
Zero conditional
This is used when there is no condition; in other words you could substitute ‘if’ with ‘when’. It is often used when describing facts or explaining how something works.
Structure: if + present • present
If you don’t water flowers, they die.
If you turn that switch to the black position, the power gets cut off.
If you mix water with oil, the oil floats.
1st conditional
The first conditional is used for situations based on facts. The condition describes something normal and possible, and the result is probable and based on the present or the future.
Structure: if + (any) present • future/imperative/modal verb
If you study hard, you will pass your exams.
If you click on that icon, you’ll lose anything you haven’t saved.
If it doesn’t rain tomorrow, we’re going to the beach.
If you’ve finished, you may go.
If you’ve finished , close your books!
If it’s raining, don’t go out!
2nd conditional
This conditional is not based on facts. It refers to a situation in the present or future which is unreal, unlikely or contrary to facts. To show this unreality, we have to shift the tense from the present to the past, although the condition still refers to the present or the future.
Structure: if + past (simple/continuous) • would (or could, or might) + infinitive
If I won the lottery, I would buy a fast car.
If I had some money, I would/might give you some (“but I haven’t got any money, so you can’t have any”).
If I were(1) you, I wouldn’t do it (“I’m not you, it’s a piece of advice”).
If that car were(2) cheaper, I would buy it. (Not “If that car was cheaper…”).
If you were paying attention, you would know what I’m talking about. (“I can see you’re not paying attention”)
(1) “If I were you, …” is an expression. (Don’t use “If I was you, …”)
(2) In unreal conditionals the form “was” is not considered grammatically correct. In written English or in testing situations, you should always use “were.” However, in everyday conversation, “was” is often used.
3rd conditional
The third conditional refers to situations in the past which, because they’re in the past, are imaginary or impossible. You can’t change the past.
Structure: if + past perfect • would (or could, or might) have + past participle
If I had studied more, I would have passed my exams (“but I went out every night with my friends, didn’t open a book, and I failed”).
If I hadn’t spent all my money on CDs I could have given some to you (“but I did spend it on CDs and I wouldn’t give you any money anyway”).
If you had been ready on time, we wouldn’t have missed the train and we would have arrived before all the restaurants closed (“but you were too slow and now we’re hungry and there’s nowhere open”).
Mixed Conditionals
With this combination we are talking about how an imagined or real event in the past would affect our present situation.
If I had won the lottery, I would be rich. (But I didn’t win the lottery in the past and I am not rich now)
If I had taken French in high school, I would have more job opportunities. (But I didn’t take French in high school and I don’t have many job opportunities)
If she had been born in the United States, she wouldn’t need a visa to work here. (But she wasn’t born in the United States and she does need a visa now to work here)
They refer to an unreal present situation and its probable (but unreal) past result.
If I were rich, I would have bought that Ferrari we saw yesterday. (But I am not currently rich and that is why I didn’t buy the Ferrari yesterday)
If Sam spoke Russian, he would have translated the letter for you. (But Sam doesn’t speak Russian and that is why he didn’t translate the letter)
If didn’t have to work so much, I would have gone to the party last night. (But I have to work a lot and that is why I didn’t go to the party last night)