THE ENGLISH CONDITIONAL ALL IN ONE FULL EXPLANATION

THE FIRST CONDITIONAL SENTENCE

The first conditional has the present simple after 'if', then the future simple in the other clause:

IF + SUB + V1+ (OBJ) , + SUB + WILL+ BASE FORM + (OBJ) OR SUB + WILL+ BASE FORM + (OBJ) + IF + SUB + V1+ (OBJ)

It's used to talk about things which might happen in the future. Of course, we can't know what will happen in the future, but this describes possible things, which could easily come true.

For example:

If it rains, I won't go to the park.

If I study today, I'll go to the party tonight.

If I have enough money, I'll buy some new shoes.

She'll be late if the train is delayed.

She'll miss the bus if she doesn't leave soon.

If I see her, I'll tell her.

1: First vs. Zero Conditional:

The first conditional describes a particular situation, whereas the zero conditional describes what happens in general.
For example (zero conditional):

if you sit in the sun, you get burned (here I'm talking about every time a person sits in the sun - the burning is a natural consequence of the sitting)
But (first conditional): if you sit in the sun, you'll get burned (here I'm talking about what will happen today, another day might be different)

2: First vs. Second Conditional:

The first conditional describes things that I think are likely to happen in the future, whereas the second conditional talks about things that I don't think will really happen. It's subjective; it depends on my point of view.
For example (first conditional):

If she studies harder, she'll pass the exam (I think it's possible she will study harder and so she'll pass)
But (second conditional): If she studied harder, she would pass the exam (I think that she won't study harder, or it's very unlikely, and so she won't pass).

THE SECOND CONDITIONAL SENTENCE

The second conditional uses the past simple after if, then 'would' and the infinitive:

IF + SUB + V­2 + (OBJ) + , + SUB + WOULD + BASE FORM + (OBJ)

(We can use 'were' instead of 'was' with 'I' and 'he/she/it'. This is mostly done in formal writing).

IT HAS TWO USES.

First, we can use it to talk about things in the future that are probably not going to be true. Maybe I'm imagining some dream for example.

If I won the lottery, I would buy a big house.(I probably won't win the lottery)

If I met the Queen of England, I would say hello.

She would travel all over the world if she were rich.

She would pass the exam if she ever studied.(She never studies, so this won't happen)

Second, we can use it to talk about something in the present which is impossible, because it's not true. Is that clear? Have a look at the examples:

If I had his number, I would call him. (I don't have his number now, so it's impossible for me to call him).

If I were you, I wouldn't go out with that man.

How is this different from the first conditional?

This kind of conditional sentence is different from the first conditional because this is a lot more unlikely.
For example (second conditional): If I had enough money I would buy a house with twenty bedrooms and a swimming pool (I'm probably not going to have this much money, it's just a dream, not very real)
But (first conditional): If I have enough money, I'll buy some new shoes (It's much more likely that I'll have enough money to buy some shoes).

THE THIRD CONDITIONAL SENTENCES

We make the third conditional by using the past perfect after 'if' and then 'would have' and the past participle in the second part of the sentence:

IF + SUB + HAD + V­3+ (OBJ) +, + SUB + WOULD + HAVE + V3+ (OBJ)

It talks about the past. It's used to describe a situation that didn't happen, and to imagine the result of this situation.

For example:

If she had studied, she would have passed the exam (but, really we know she didn't study and so she didn't pass)

If I hadn't eaten so much, I wouldn't have felt sick (but I did eat a lot, and so I did feel sick).

If we had taken a taxi, we wouldn't have missed the plane

She wouldn't have been tired if she had gone to bed earlier

She would have become a teacher if she had gone to university

He would have been on time for the interview if he had left the house at nine.

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