( From Oxford Practice Grammar )
Lets take a look at conditional sentences:
There are four types of conditional sentences that each expresses a different degree of probability
▪ Zero conditional
▪ First conditional
▪ Second conditional
▪ Third conditional
➡ All about zero conditional
Zero conditional sentences express general truths:situations in which one thing “always”causes another. When you use a zero conditional, you’re talking about a general truth rather than a specific instance of something. Consider the following examples:
✅ If you don’t brush your teeth, you get cavities.
✅if the water reaches 100degrees celcius it boils
🌸First, when using the zero conditional, the correct tense to use in both clauses is the simple present tense. A common mistake is to use the simple future tense.
🌸second: , notice that the words if and when can be used interchangeably in these zero conditional sentences. This is because the outcome will always be the same, so it doesn’t matter “if” or “when” it happens.
➡ All about first conditional:
First conditional sentences are used to express situations in which the outcome is likely (but not guaranteed) to happen in the future. Look at the examples below:
✅If you rest, you will feel better.
✅If you set your mind to a goal, you’ll eventually achieve it.
❌Note that we use the simple present tense in the if-clause and simple future tense in the main clause ,that is, the clause that expresses the likely outcome. This is how we indicate that under a certain condition (as expressed in the if-clause), a specific result will likely happen in the future.
✅✅✅✅ : Use the zero conditional (i.e., simple present + simple present) only when a certain result is guaranteed. If the result is likely, use the first conditional (i.e., simple present + simple future
➡ All about second conditional
Second conditional sentences are useful for expressing outcomes that are completely unrealistic or will not likely happen in the future. Consider the example below:
✅If I inherited a billion dollars, I would travel to the moon.
❌the correct way to structure second conditional sentences is to use the simple past tense in the if-clause and an auxiliary modal verb (e.g., could, should, would, might) in the main clause (the one that expresses the unrealistic or unlikely outcome)
✅When applying the second conditional, use the simple past tense in the if-clause.
✅Use a modal auxiliary verb in the main clause when using the second conditional mood to express the unlikelihood that the result will actually happen.
➡ All about third conditional
Third conditional sentences are used to explain that present circumstances would be different if something different had happened in the past. Look at the following examples:
✅If you had told me you needed a ride, I would have left earlier.
✅If I had cleaned the house, I could have gone to the movies.
❗️These sentences express a condition that was likely enough, but did not actually happen in the past.
❌ Note that when using the third conditional, we use the past perfect (i.e., had + past participle) in the if-clause.
The modal auxiliary (would, could, shoud, etc.) + have + past participle in the main clause expresses the theoretical situation that could have happened.