If (2)

Third conditional

If clause                                     Main clause

If + Past Perfect                          would have

We use the Third conditional to talk about things in the past happening differently from the way they really happened.

• If I had worked harder I would have passed the exam. (But I didn't work hard, and I didn't pass the exam.)
• If it had rained last weekend,  we would have stayed at home. ( but it didn’t rain last weekend)
• If I had woken up on time, I would have taken the bus. (What really happened was that I didn't wake up on time, and so I didn't take the bus.)
• You could have arrived on time if you had used a map.
• We might have finished the work on time if they had helped us last week.
• If you hadn't lied to me before, I would have believed you.

If

First Conditional

If clause                                    Main clause

If + Present Simple                       will

The present tense refers to a possible future action, something which may or may not happen.

• If I have money, I will buy a car.
• If we hurry, we will catch the bus.
• If it rains, we will stay at home.

 The main clause often has will. But we can use other modal verbs.

• If he helps me, I may finish the project on time.
• If you don’t feel well, you must go to the doctor.