Conditional Sentence

Conditional Sentences are also known as Conditional Clauses or If Clauses. They are used to express that the action in the main clause (without if) can only take place if a certain condition (in the clause with if) is fulfilled. This sentence consists of two parts:
1. Main Clause (Parent sentence): the sentence can stand alone because it has a subject and predicate.
2. Sub-ordinate Clause / If clause (clause): the sentence can not stand alone / must be attached to the main clause.
There are three types of Conditional Sentences: Future Possible Condition, Present Unreal Condition, Past Unreal Con-dition.
Type I condition: Future Possible Conditional
Future possible conditional is a conditional sentence, that is, if the occurrence of a case depends on whether the conditions are met or not.
This type refers to an action or event that will only happen in the future if requirements are met. we actually do not know whether the requirements are being met or not, but the terms or conditions are still very realistic that we can think that the assumption that we make possible.
Example:
1. If there are no starts, the sky will be very dark.
Fact: possibility of the sky is not so dark, when there will be a star.
2. If you eat too much, you will get a stomachache.
Fact : he did not eat much because he did not want to upset stomach
Tenses:
If clause Result clause
If + Simple Present Simple Future
Formula :
S + will + V1 + if + S + V1/V1+s/es
or
If + S + V1/ V1+s/es , S + will + V1
Description:
Clause if it can be placed at the beginning of the sentence without changing the meaning, but the second sentence should be preceded by a comma (,)
Note: In this type, "if" is often replaced with "when"

Type II condition: Present Conditional
Different from the future conditional, conditionals present conditional is used to express a state that is not possible be fulfilled. Present conditional shows the current situation. Unfortunately, we expect different things that happen, or imagining events that occur otherwise.
Example :
1. If I went to Jakarta, I would visit him.
Fact : I don’t go to Jakarta.
2. If he didn’t drink beer, he wouldn’t get drunk.
Fact : He drinks beer.
3. If I passed the exam, I would continue to university.
Fact : I do not pass the exam now.
Tenses:
If clause Result clause
If + Simple Past Past Future Tense

Formula :
IF + S + V2, S + would + V1
Note:
In type II “were “ is used for all subjects
Example :
If I were you, I would continue to university ( but I am not you).
Were as the only “be”
In the present conditional, the verb "be" in the if clause has always been "were" and never become "was". any subject of the sentence. "was" beginning to be used only in colloquial language.
Example:
Result Clause If Clause
I would buy a farm. If I were rich.
S “be”
NOT
If I was rich
She would act in a horror movie. If she were an artist.
We would go to see Monas. If we were in Jakarta.





Type III condition: Past Conditional
Past conditional sentence is also an assumption that is not possible be fulfilled. This type refers to a situation that has happened in the past and obviously could not change. So, we can only assume if it is different even though we already know it is impossible supposition.
Example:
1. If I had locked the door, the thieves would not have been able to get in.
Fact : I didn’t lock the door.
2. If the weather had been fine, we could have gone to the zoo.
Fact : The weather wasn’t fine.
3. If I had passed the exam, I would have continued to university.
Fact : I did not pass the exam then.
Tenses:
If clause Result clause
Past Perfect Tense Past Future Perfect Tense

Formula :
IF + S + had + V3, S + would have + V3
Note:
For type III often shaped inversion (reversal), two subjects and verbs do not use the IF.




Source :
Utami, puput- Tim Bahasa ILT. PT. Bhuana Ilmu Populer. Jakarta. 2011
http://adivampciel.blogspot.com/2011/11/conditional-sentences.html
http://nonaqoe.wordpress.com/2008/07/10/conditional-sentence/