There are four basic types of conditional sentences. Each one of them has two parts: an “if” clause (condition) and a main clause (result).
When the sentence starts with the “if” clause, the two parts of the sentence are separated by a comma. But when the main clause is at the beginning, we don’t use one.
Zero Conditional
We use it to talk about things which are always true — such as scientific facts and general truths.
• If you heat water to 100 degrees, it boils.
• If you mix blue and yellow, you get green.
First Conditional
We use it to talk about things which are possible in the present or the future — things which may happen. You can also give some advice.
• If you don’t have a map, you will get lost.
• If you have a headache, take an aspirin.
• If you go to Paris, you should visit the Eiffel Tower.
Second Conditional
We use it to talk about something that does not apply to the present and it is not very likely to happen in the future.
• If he had the book, he would lend it to me.
• If you had wings, you could fly like Peter Pan.
• If he went to London, he might see the Queen.
Third Conditional
We use it to talk about things which didn’t happen in the past. We imagine how things would have been if something different had happened. We can also use the third conditional to express criticism or regret.
• If we arrived earlier, we wouldn’t have missed the beginning of the concert.
• If your team had played better, you could have won the match.
• If Susan had been more careful, she might not have broken the glass.
TIP
In the ZERO conditional we can use when instead of if.
• When you heat water to 100 degrees, it boils.
In the FIRST conditional, we can use unless (=if not) instead of if. Remember that “unless” is never followed by a verb in the negative form.
• Unless it rains soon, all the plants will die.
We can also use provided (that), providing (that), as soon as, as long as or so long as instead of if.
• You can borrow my car provided that you bring it back today.
• I’ll be home at eight as long as my train arrives on time.
REMEMBER
Sometimes there is a connection between past hypothetical conditionals and the present. In this case we use the “if” clause from the THIRD CONDITIONAL and the main clause from the SECOND CONDITIONAL. This type of conditional sentence is called a MIXED CONDITIONAL.
• If you had gone to bed earlier, you wouldn’t be so tired.
