If is a conjunction. We use it to express a condition.
- If you arrive early, we can go to the movies.
- If she is late, we will go without her.
- If I win this championship, my parents will be proud of me.
- If you are hungry, I will get you something to eat.
Since ‘if’ expresses a condition, sentences using if are often called conditional sentences.
There are mainly four types of conditional sentences in English.
- Zero conditional
- First conditional
- Second conditional
- Third conditional
The zero conditional is used to talk about general facts or truths. In the zero conditional, we use the simple present tense in both clauses.
If you heat ice, it melts.
If you give respect, you get respect.
The first conditional is used to talk about real and possible situations.
In the first conditional, we use a simple present tense in the if-clause and will / can / may + infinitive (first form of the verb) in the result clause.
- If she comes, I will show her my work.
- If you ask more politely, she will help you.
- If you eat too much, you will fall ill.
- If it rains, we will cancel the trip.
- If I fail my test, my mother will be upset.
The second conditional is used to talk about imaginary situations. In the second conditional, we use a simple past tense in the if-clause and would / could / might + infinitive in the main clause.
- If she came, I would show her my work. She didn’t come and I didn’t show her my work, but if she had come I would have shown her. As you can see, we are talking about an unreal situation here.
More examples are given below.
- If you asked more politely, she would help you.
- If you ate too much, you would fall ill.
- If it rained, we would cancel the trip.
- If I failed my test, my mother would be upset.
The third conditional is used to talk about imaginary or hypothetical situations. There isn’t much difference between second and third conditional. However, structures are different. In the third conditional, we use a past perfect tense in the if-clause and would have + past participle in the main clause.
- If she had come, I would have shown her my work.
- If you had asked more politely, she would have helped you.
- If you had eaten too much, you would have fallen ill.
- If it had rained, we would have cancelled the trip.
- If I had failed my test, my mother would have been upset.