If Conditional

http://www.edufind.com/english/grammar/if_conditional1.php

There are four main types of 'if' sentences in English:

1. The 'zero' conditional, where the tense in both parts of the sentence is the simple present:

'IF' CLAUSE	MAIN CLAUSE
If + simple presentIf you heat ice If it rains	simple presentit melts. you get wet

In these sentences, the time is now or always and the situation is real and possible. They are often used to refer to general truths.

2. The Type 1 conditional, where the tense in the 'if clause is the simple present, and the tense in the main clause is the simple future

'IF' CLAUSE	MAIN CLAUSE
If + simple presentIf it rains If you don't hurry	Simple futureyou will get wet we will miss the train.

In these sentences, the time is the present or future and the situation is real. They refer to a possible condition and its probable result.

3. The Type 2 conditional, where the tense in the 'if' clause is the simple past, and the tense in the main clause is the present conditional:

'IF' CLAUSE	MAIN CLAUSE
If + simple pastIf it rained If you went to bed earlier	Present conditionalyou would get wet you wouldn't be so tired.

In these sentences, the time is now or any time, and the situation is unreal. They are notbased on fact, and they refer to an unlikely or hypothetical condition and its probable result.

4. The Type 3 conditional, where the tense in the 'if' clause is the past perfect, and the tense in the main clause is the perfect conditional:

'IF' CLAUSE	MAIN CLAUSE
If + past perfectIf it had rained If you had worked harder	Perfect conditionalyou would have got wet you would have passed the exam.

In these sentences, the time is past, and the situation is contrary to reality. The facts they are based on are the opposite of what is expressed, and they refer to an unreal past condition and its probable past result.

A further type of 'if' sentence exists, where Type 2 and Type 3 are mixed. The tense in the'if' clause is the past perfect, and the tense in the main clause is the present conditional:

'IF' CLAUSE	MAIN CLAUSE
If + past perfectIf I had worked harder at school If we had looked at the map	Present conditionalI would have a better job now. we wouldn't be lost.

In these sentences, the time is past in the 'if' clause, and present in the main clause. They refer to an unreal past condition and its probable result in the present.