Conditional Clauses

Conditional forms are used to imagine events in certain conditions. The conditional can be used to speak about real events that always happen (first conditional), imaginary events (second conditional), or imagined past events (third conditional). Conditional sentences are also known as 'if' sentences. 

Here are some examples:

If we finish early, we will go out for lunch. - First conditional - possible situation
If we had time, we would visit our friends.

- Second conditional - imaginary situation
If we had gone to New York, we would have visited the exhibit. - Third conditional - past imagined situation

English learners should study conditional forms to speak about past, present and future situations that depend on other events happening. There are four forms of the conditional in English. Students should study each of the forms to understand how to use conditionals to speak about:

• Something that is always true if something happens - conditional zero
• Something that will be true in the future if something happens - conditional one or real conditional
• Something that would be true if something happened in the present - conditional two or unreal conditional
• Something that would have been true in the past if something had happened - conditional three or unreal conditional

At times it might be difficult to make the choice between the first and second (real or unreal) conditional form. You can study this guide to the first or second conditional for more information on making the proper choice between these two forms.

Once you have studied conditional structures, practice your understanding of the conditional forms by taking the conditional forms quiz. Teachers can also use the printable conditional forms quiz in-class.

Listed below are examples, uses and formation of Conditionals followed by a quiz.

Conditional 0

Situations that are always true if something happens.

NOTE

This use is similar to, and can usually be replaced by, a time clause using 'when' (example: When I am late, my father takes me to school.)

If I am late, my father takes me to school.
She doesn't worry if Jack stays out after school.

Conditional 0 is formed by the use of the present simple in the if clause followed by a comma the present simple in the result clause.

You can also put the result clause first without using a comma between the clauses.

If he comes to town, we have dinner.
OR
We have dinner if he comes to town.

Conditional 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.

NOTE

In the conditional 1 we often use unless which means 'if ... not'. In other words, '...unless he hurries up.' could also be written, '...if he doesn't hurry up.'.

If it rains, we will stay at home.
He will arrive late unless he hurries up.
Peter will buy a new car, if he gets his raise.

Conditional 1 is formed by the use of the present simple in the if clause followed by a comma will verb (base form) in the result clause. You can also put the result clause first without using a comma between the clauses.

If he finishes on time, we will go to the movies.
OR
We will go to the movies if he finishes on time.

Conditional 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.

NOTE

The verb 'to be', when used in the 2nd conditional, is always conjugated as 'were'.

If he studied more, he would pass the exam.
I would lower taxes if I were the President.
They would buy a new house if they had more money.

Conditional 2 is formed by the use of the past simple in the if clause followed by a comma would verb (base form) in the result clause. You can also put the result clause first without using a comma between the clauses.

If they had more money, they would buy a new house.
OR
They would buy a new house if they had more money.

Conditional 3

Often referred to as the "past" conditional because it concerns only past situations with hypothetical results. Used to express a hypothetical result to a past given situation.

If he had known that, he would have decided differently.
Jane would have found a new job if she had stayed in Boston.

Conditional 3 is formed by the use of the past perfect in the if clause followed by a comma would have past participle in the result clause. You can also put the result clause first without using a comma between the clauses.

If Alice had won the competition, life would have changed OR Life would have changed if Alice had won the competition.

Source: http://esl.about.com/od/gramma1/a/conditional.htm