Comparison of conditional tenses
As part of our series examining time clauses, in this lesson we will look at the grammar of conditional sentences. Conditional sentences have two clauses; a condition (expressed by 'if') and a result (an action). The action will only take place if the condition is met.
There are four types of conditionals. Here we will look at the differences between them, and give an explanation and examples of when and how each type is used.
This type of conditional is used to describe things that will always be true when the condition of the 'if' clause is met.
Form of zero conditional
The same verb form is used in both parts of the sentence: the simple present tense.
Use of zero conditional
The zero conditional is used for scientific facts and things we are certain of.
The meaning of this kind of sentence remains the same if 'when' is substituted for 'if'.
If ice cream gets hot, it melts.
(We know that under the condition 'the ice cream gets hot', the result 'it melts' will always happen.)
If Peter doesn't sleep enough, he gets tired.
(This will always be true when Peter cannot get enough sleep.)
If the battery runs out, the torch stops working.
(We know the torch cannot run without batteries.)
This type of conditional is used to talk about things that we believe will happen in the future.
Form of the first conditional
In a first conditional sentence, we use the present simple verb form for the condition clause, then 'will' and the infinitive for the result.
Use of the first conditional
Although the action is in the future, the condition clause must be in the present tense.
We don't know what will happen in the future, but the first conditional is used to discuss things things that are likely to happen.
If the action is unlikely to happen, the second conditional is a better form to use.
If Daniel comes to visit, we will have tea.
(In this example, the condition - Daniel comes to visit - is in the future, and is likely to happen, bringing the result; tea. Note that although the event is in the future, the present tense is used, so 'If Daniel will come to visit...' would be incorrect.)
If it looks like rain this afternoon, I will take an umbrella.
(There is a chance of rain in the afternoon.)
If Manchester United win, Sarah will be happy.
(It is possible that this football team will win.)
The second conditional is used to talk about impossible and imaginary situations in the future.
Form of the second conditional
In a second conditional sentence, we use the past simple for the condition clause, then 'would' and the infinitive for the result.
Use of the second conditional
Although the action is in the future, the condition clause must be expressed in the past tense.
The words 'should', 'could' and 'might' can be used instead of 'would' in a second conditional sentence.
If the action described in the result clause is likely to happen, you should use the first conditional instead.
If Manchester was closer to London, I would visit my cousin more often.
(The two cities cannot move closer together.)
If Lisa didn't have to work at the bank tomorrow, she would play tennis instead.
(But she must work at the bank tomorrow.)
If caviar were cheaper, I would eat it every day.
(The condition is a lower price than the current one.)
In third conditional sentences we talk about situations that did not happen in the past, and what the result would have been.
Form of the third conditional
We use the past perfect tense for the condition clause, then 'would have' and the past participle for the result clause.
Use of the third conditional
The third conditional always talks about an imaginary past that did not happen.
Both the condition and the result must be impossible in a third conditional clause.
If it had rained, I would have got wet.
(In this example, the real situation is that it did not rain.)
If John had proposed marriage, I would have said yes.
(He didn't propose marriage.)
If Catherine had played the drums, I would have danced.
(She did not play the drums.)