CONDITIONAL SENTENCE

Conditional tenses are used to speculate about what could happen, what might have happened, and what we wish would happen. In English, most sentences using the conditional contain the word if. Many conditional forms in English are used in sentences that include verbs in one of the past tenses. This usage is referred to as "the unreal past" because we use a past tense but we are not actually referring to something that happened in the past. There are five main ways of constructing conditional sentences in English. In all cases, these sentences are made up of an if clause and a main clause. In many negative conditional sentences, there is an equivalent sentence construction using "unless" instead of "if".

Conditional Sentence Type	Usage	If clause verb tense	Main clause verb tense
Type 1	A possible condition and Its probable result	Simple present	Simple future
Type 2	A hypothetical condition and its probable result	Simple past	Present conditional or present continous conditional
Type 3	An unreal past condition and its probable result in the past	Past perfect	Perfect conditional

TYPE 1 CONDITIONAL

The type 1 conditional is used to refer to the present or future where the situation is real. The type 1 conditional refers to a possible condition and its probable result. In these sentences the if clause is in the simple present, and the main clause is in the simple future.

Form:    if + Simple Present, will-Future

Example :

1.  If I have enough money, I will buy a car.
2. If you study hard, you will pass the exam.
3. If he doesn’t hurry, he will late.

TYPE 2 CONDITIONAL

The type 2 conditional is used to refer to a time that is now or any time, and a situation that is unreal. These sentences are not based on fact. The type 2 conditional is used to refer to a hypothetical condition and its probable result. In type 2 conditional sentences, the if clause uses the simple past, 

and the main clause uses the present conditional.

Form:    if + Simple Past, Conditional I (= would + Infinitive)

Example :

1. If i lost my wallet, i would not buy this guitar.
2. If they had not enough skill, they would not win this game.
3. If you passed the exam, you would not miss this class

TYPE 3 CONDITIONAL

The type 3 conditional is used to refer to a time that is in the past, and a situation that is contrary to reality. The facts they are based on are the opposite of what is expressed. The type 3 conditional is used to refer to an unreal past condition and its probable past result. In type 3 conditional sentences, the if clause uses the past perfect, and the main clause uses the perfect conditional.

Form:    if + Past Perfect, Conditional II (= would + have + Past Participle)

Example :

1. If the weather is nice tomorrow, we would have played football.
2. If I had accepted that invitation, I would have gone to the party.
3. If you had found her bracelet, you  would not  have given her a new bracelet .

Sumber :

·         http://www.edufind.com/english-grammar/conditional/

·         https://www.ego4u.com/en/cram-up/grammar/conditional-sentences