Sentences containing the word if are called conditional sentences because they usually express a condition.
- If he comes, ask him to wait.
- If it rains, we will get wet.
- If you study hard, you will pass your exam.
There are four types of if sentences in English.
- The zero conditional
- The type 1 conditional
- The type 2 conditional
- The type 3 conditional
The zero conditional
In a zero conditional sentence, we use a present tense in both parts of the sentence.
- If you give respect, you get respect.
- If you heat ice, it melts.
The type zero conditional sentences are used to talk about real and possible situations.
Type 1 conditional
Type 1 conditional sentences are used to talk about possible situations and their probable results. In these sentences we use the simple present in the if clause and the simple future in the result clause.
- If you work hard, you will succeed.
- If you ask him, he will help you.
- If you invite them, they will come.
Type 2 conditional
These sentences are used to talk about an unlikely condition and its probable result. Here the tense in the if clause is the simple past and the tense in the main clause is the present conditional (would + get).
- If you asked him, he would help you.
- If you studied hard you would pass your exam.
- If you invited them, they would come.
Type 3 conditional
In a type 3 conditional sentence, the tense in the if clause is the past perfect and the tense in the main clause is the perfect conditional (would have + infinitive).
- If you had invited them, they would have come.
- If you had asked him, he would have helped you.