CONDITIONAL SENTENCE TYPE 0, 1, 2 and 3

Conditional Sentence Type 0

Conditional type zero is used to talk about general truths, scientific facts or things which always happen under certain conditions.

Form:

If + Simple Present, + Simple Present

Use:

The zero conditional is used to talk about things which are always true, scientific facts, general truths:
Examples:

If you cross an international date line, the time changes.
Phosphorus burns if you expose it to air.
If I wake up early, I go jogging.
NOTE: you can use "when" instead of "if".

Conditional Sentence Type 1

Often called the "real" conditional because it is used for real or possible situations. These situations take place if a certain condition is met. It is possible and also very likely that the condition will be fulfilled.

Form:

If + Simple Present, + Simple Future

Use

Conditional Sentences Type 1 refer to the future. An action in the future will only happen if a certain condition is fulfilled by that time. We don't know for sure whether the condition actually will be fulfilled or not, but the conditions seems rather realistic – so we think it is likely to happen.
Example:

If I have enough time, I'll watch the football match.

I may have time to watch the match but I'm not sure about it.

 

Conditional Sentence Type 2

Often called the "unreal" conditional because it is used for unreal impossible or improbable situations. This conditional provides an imaginary result for a given situation. It is very unlikely that the condition will be fulfilled.

Form:

if + Simple Past, + would + base verb

Were / Was

In conditional type 2, we usually use in the if clause "were" instead of "was" even if the pronoun isI, he, she or it. "were" here is a subjunctive form.
NOTE "was" is also a possible form.

Example:

If I were a millionaire, I would buy a castle.

Use

Conditional Sentences Type 2 refer to an action in the present that could happen if the present situation were different. I don't really expect the situation to change because it is very unlikely.

Example:

If I had a lot of money, I would travel around the world.

Conditional Sentence Type 3

It is impossible that the condition will be met because it refers to the past.

Form:

if + Past Perfect, + would + have + Past Participle

Use

Conditional Sentences Type 3 refer to situations in the past. They express hypothetical results to past given situations.

Example:

If he had been careful, he wouldn't have had that terrible accident.
Sometimes in the past, he was careless. He drove so fast. So he had a terrible accident

Things to remember

1. The main clause can also be at the beginning of the sentence. In this case, don't use a comma.

Examples:

"Phosphorus burns if you expose it to air."
" I will send her an invitation if I find her address."
" I would travel around the world if I had a million dollars."
"He wouldn't have had that terrible accident if he had been careful."

2. Main clause and/or if clause might be negative.

Example:

If I don’t see him this afternoon, I will phone him in the evening.
If he had been careful, he wouldn't have had an accident.