We use special tenses with if to talk about unreal situations.
Unreal or improbable present or future situations
To talk about unreal or improbable present or future situations, we use a past tense in the if-clause and would + infinitive in the result clause.
- If you asked her, she would tell you. (NOT If you ask her, she would tell you.) (NOT If you would ask her, she would tell you.)
Here we are talking about an unreal situation. Neither of the two actions mentioned in the two clauses actually took place.
More examples are given below:
- If John invited Mary, she would come. (= John didn’t invite Mary, but if he had invited her, she would have come.)
- If he stopped smoking, he wouldn’t get cancer.
- If you helped her, she would be happy.
Instead of would, we can use could and might. In this case, could means ‘would be able to’ and might means ‘would perhaps’.
- If you lent me a dollar, I could buy something to eat. (= If you lent me a dollar, I would be able to buy something to eat.)
- If you asked her more politely, she might help you. (= If you asked her more politely, she would perhaps help you.)