There are mainly three sentence patterns with if. In grammars, these are often called ‘first’ conditional, ‘second’ conditional and ‘third’ conditional.

The first conditional sentences are used to talk about real and possible situations. Here we use a simple present tense in the if-clause and will + infinitive in the result clause.

If you work hard, you will win.

If you invite her, she will come.

The second conditional is used to talk about unreal and improbable situations. Here we use a past tense in the if-clause and would + infinitive in the result clause.

If you worked hard, you would win.

If you invited her, she would come.

Difference between first conditional and second conditional sentences

Difference between first conditional and second conditional is not a difference of time. Both structures can refer to the present or future; the second conditional simply suggests that a situation is impossible or imaginary.

Compare:

If I win the first prize, I will be perfectly happy. (Said by someone who has good chances of winning.)

If I won the first prize, I would be perfectly happy. (Said by someone who has no chances of winning.)

Second conditional sentences are also used to make a request sound more polite.

Compare:

Will it be alright if I take your car? (Direct request)

Would it be alright if I took your car? (More polite request)