In the English language, like in many other languages, there are conditional sentences. They can express both real and unrealistic conditions. The «if» conjunction helps make a conditional sentence in English.
The types of conditional sentences
There are 4 types of conditional sentences — Zero type, the First, the Second and the Third conditionals. Also, mixed type sentences are mentioned in a separate rule.
Application: are used to emphasize truthfulness or simply to express a scientific fact or obvious statements. You can also use them to indicate instructions and orders.
Conditions: real — events can happen. Since the sentence is 100% true and real, you must use the Present Simple of the verb. Also, in this type of a sentence, the «if» conjunction can be replaced with «when».
[If + Present Simple] + [Present Simple] If you heat water, it boils. If you wear glasses, you see better.
The First Conditional
Application: Sentences of this type can refer to both the present and the future, since we are talking about events that take place in the present, or under certain conditions may occur in the future.
Conditions: real — events can happen in the present and in the future.
[If + Present Simple] + [Future Simple] If you buy a car, you will go to work in time. If you wear glasses, you will look perfect.
The Second Conditional
Application: «unreal present» — this is the name of this type of conditional sentences, because it reflects an unreal situation, related to the present or future time. Also, sentences of the second type can be used when you want to give advice to someone.
Conditions: virtually unrealistic, the probability of such a situation is very small, but it is not excluded by 100%.
[If + Past Simple] + [would / could / should + verb] If I were an actress, I would get an Oscar. If you were a millionaire, you could buy Lamborghini.
The Third Conditional
Application: we use this type of conditional sentences when talking about events that could happen, but did not happen. Also, such sentences are called «the unreal past»; more often these phrases transfer a regret about what took place or did not happen. Also, we use this type of sentences if we want to criticize actions taken in the past.
Conditions: unrealistic, because events happened in the past and they cannot be changed anymore.
[If + Past Perfect] + [would / could / should + have + V3 / -ed]
If you had been prepared for this exam, you would have passed it. If you had not forgotten your iPhone here, it would not have been stolen.