There are different types of conditions. Some are possible or likely, others are unlikely, and others are impossible:
If the weather improves, we’ll go for a walk. (It is possible or likely that the weather will improve.)
If the weather improved, we could go for a walk.(It is not likely that the weather will improve.)
If the weather had improved, we could have gone for a walk. (The weather did not improve – fine weather is therefore an impossible condition.)
These types of conditions are used in three types of sentences, called first, second and third conditional sentences.
Imagined conditions: the first conditional
We use the first conditional to talk about the result of an imagined future situation, when we believe the imagined situation is quite likely:
[imagined future situation]If the taxi doesn’t come soon, [future result]I’ll drive you myself.
First conditional: form
We use the modal verb in the main clause, not in the conditional clause.
If a lawyer reads the document, we will see if we’ve missed anything important.
If a lawyer will read the document…
Imagined conditions: the second conditional
We use the second conditional to talk about the possible result of an imagined situation in the present or future. We say what the conditions must be for the present or future situation to be different.
If people complained, things would change.(People don’t complain at themoment.)
Second conditional: form
We use a past form in the conditional clause to indicate a distance from reality, rather than indicating past time. We often use past forms in this way in English.
We use would in the main clause, not in the conditional clause:
If you decided to take the exam, you would have to register by 31 March.
If you would decide to take the exam…
First and second conditional compared
When we use the first conditional, we think the imagined situation is more likely to happen than when we use the second conditional.
Imagined conditions: the third conditional
We use the third conditional when we imagine a different past, where something did or did not happen, and we imagine a different result:
If I had played better, I would have won. (I didn’t play well and I didn’t win.)
It would have been easier if George had broughthis own car. (George didn’t bring his own car, so the situation was difficult.)
If the dog hadn’t barked, we wouldn’t have known there was someone in the garden. (The dog barked, so we knew there was someone in the garden.)
Third conditional: form
We use would have + -ed in the main clause, not in the conditional clause:
If he had stayed in the same room as Dave, it would have been a disaster.
If he would have stayed… it would have been a disaster.
People do sometimes use the form with would have in informal speaking, but many speakers consider it incorrect.
Some conditions seem more real to us than others. Real conditionals refer to things that are true, that have happened, or are very likely to happen:
If you park here, they clamp your wheels. (It is always true that they clamp your wheels if, or every time, you park here.)
If I can’t sleep, I listen to the radio. (it is often true that I can’t sleep, so I listen to the radio)
In real conditional sentences, we can use the present simple or present continuous in both clauses for present situations, and the past simple or past continuous in both clauses for past situations. We can use these in various different combinations.
Present simple + present simple
If the weather is fine, we eat outside on the terrace. (Every time this happens, this is what we do.)
Present continuous + present simple
If the kids are enjoying themselves, we just let them go on playing till they’re ready for bed. (Every time this happens, this is what we do.)
Present continuous + present continuous
If the economy is growing by 6%, then it is growing too fast. (If it is true that the economy is growing by 6%, then it is true that it is growing too fast.)
Past simple + past simple
If my father had a day off, we always went to see my granddad. (Every time that happened in the past, that is what we did.)
Past simple + past continuous
Kevin always came in to say hello if he was goingpast our house. (Every time he was going past our house, that is what he did.)
We can also use modal verbs in the main clause:
If we go out, we can usually get a baby sitter.(Every time we go out, it is usually possible to get a babysitter.)
If we wanted someone to fix something, we would ask our neighbour. He was always ready to help.(Every time we wanted someone, we would ask our neighbour.)