Grammar notes: conditionals
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.
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 simple, present simple
If you don't water flowers, they die.
If you heat water, it boils .
If you mix water with oil, the oil floats.
The first conditional is used for situations based on fact. The condition describes something normal and possible, and the result is probable and based on the present or the future.
Structure: if + present simple, future
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. (present used as future).
This conditional is not based on fact. 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, would + infinitive
If I won the lottery, I would buy a fast car (but I haven't won the lottery, so I can't buy anything).
If I had some money, I would give you some (but I haven't got any money, so you can't have any).
If Real Valladolid were a good football team, I would support them (but they're rubbish, so I don't).
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 (could/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).