Conditional sentences are used to describe possible results of situations that could happen in the present or future, or could have happened in the past but didn’t happen. Also, they can express general knowledge and actions that would happen in the future under certain circumstances.
Conditional sentences consist of the main clause and the subordinate clause, which is often referred to as an if - clause.
There are 4 main types of conditional sentences.
Type Zero expresses the idea that one thing causes another thing. This type is used to talk about general truths or certain situations in which the result is guaranteed. We use Present Simple in both clauses.
The structure is: If + present simple, … present simple
If you eat too much, you get fat.
If you walk on ice wearing slippery shoes, you slip and fall down.
If water is heated to 100 degrees, it boils.
Note that ‘if’ and ‘when’ are interchangeable here because the outcome will always be the same.
When you gossip about other people, you make a lot of enemies.
Type One describes specific situations which are likely to happen in the future.
The structure is: If + present simple, … future simple.
I will tell him if he comes.
If the weather is nasty tomorrow, we’ll stay home.
If I save enough money, I will buy a house.
Type Two is used to talk about things that are very unlikely in the present or probably not going to happen in the future.
The structure is: If + past simple, … would/could/should/might + bare infinitive.
If I were you, I would think everything over before making a final decision.
I would give you a lift if I had a car.
If I owned a plane, I might take all my friends to Hawaii.
Type Three is used to say that a past situation would have been different if a certain condition had happened in the past. These sentences express conditions that didn’t actually happen in the past.
The structure is: if + past perfect, would/could/might + have + past participle.
If you had told me to pick you up, I would have left earlier.
If I had washed all the dishes, I could have gone out with my friends.
She wouldn’t have felt sick if she hadn’t eaten so much cake.
There is one more type of conditionals, which is called mixed conditional sentences. It is used when the cause and the result are expressed in different time planes. For example, when the action took place in the past and has had an impact on the present, or when the present conditions have influenced actions and situations in the past.
The most common mixed conditionals are:
1. If + conditional type 3 (past), conditional type 2 (present or future).
If + past perfect, would + bare infinitive.
If I hadn’t wasted my money, I would be able to buy a new phone.
If you had studied English at school, you’d work at an international company now.
2. If + conditional type 2 (present or future), conditional type 3 (past).
If + past simple + would have + past participle.
If I didn’t have an appointment today, I would have gone out to the party with you yesterday.
If he were smarter, he would have concluded a marriage contract with her five years ago.