conditional sentences

conditional sentences
Conditional sentence
In grammar, conditional sentences are sentences discussing factual implications or hypothetical situations and their consequences. Languages use a variety of conditional constructions and verb forms (such as the conditional mood) to form such sentences.
Full conditional sentences contain two clauses: the condition or protasis, and the consequence or apodosis.
If it rains [condition], (then) the picnic will be cancelled [consequence].
Syntactically, the condition is the subordinate clause, and the consequence is the main clause. However, the properties of the entire sentence are primarily determined by the properties of the protasis (condition) (its tense and degree of factualness).
Conditional Sentence Type 1
→ It is possible and also very likely that the condition will be fulfilled.
Form: if + Simple Present, will-Future
Example: If I find her address, I’ll send her an invitation.
The main clause can also be at the beginning of the sentence. In this case, don't use a comma.
Example: I will send her an invitation if I find her address.
Note: Main clause and / or if clause might be negative. See Simple Present und will-Future on how to form negative sentences.
Example: If I don’t see him this afternoon, I will phone him in the evening.
Conditional Sentence Type 2
→ It is possible but very unlikely, that the condition will be fulfilled.
Form: if + Simple Past, Conditional I (= would + Infinitive)
Example: If I found her address, I would send her an invitation.
The main clause can also be at the beginning of the sentence. In this case, don't use a comma.
Example: I would send her an invitation if I found her address.
Note: Main clause and / or if clause might be negative. See Simple Past und Conditional I on how to form negative sentences.
Example: If I had a lot of money, I wouldn’t stay here.
Conditional Sentence Type 3
→ It is impossible that the condition will be fulfilled because it refers to the past.
Form: if + Past Perfect, Conditional II (= would + have + Past Participle)
Example: If I had found her address, I would have sent her an invitation.
The main clause can also be at the beginning of the sentence. In this case, don't use a comma.
Example: I would have sent her an invitation if I had found her address.
Note: Main clause and / or if clause might be negative. See Past Perfect and Conditional II on how to form negative sentences.
Example: If I hadn’t studied, I wouldn’t have passed my exams.

Factual
In these constructions, the condition clause expresses a condition the truth of which is unverified. The verb in the condition clause is in the past tense (with a past tense interpretation) or in the present tense (with a present or future tense interpretation). The result clause can be in the past, present, or future. Generally, conditional sentences of this group are in two groups, the "zero conditional" and the potential or indicative conditional, often called "first conditional" or "conditional 1". This class includes universal statements (both clauses in the present, or both clauses in the past) and predictions.
The "zero" conditional is formed with both clauses in the present tense. This construction is similar across many languages. It is used to express a certainty, a universal statement, a law of science, etc.:
If you heat water to 100 degrees celsius, it boils.
If you don't eat for a long time, you become hungry.
If the sea is stormy, the waves are high.
It is different from true conditionals because the introductory "if" can be replaced by "when" or "whenever" (e.g., "When you heat water..."), which cannot be done for true conditionals.
The potential or indicative conditional, often referred to as the "first conditional" or "conditional 1", is used more generally to express a hypothetical condition that is potentially true, but not yet verified. The conditional clause is in the present or past tense and refers to a state or event in the past. The result can be in the past, present, or future. Some examples with the condition clause in the past tense:
If she took that flight yesterday, she arrived at 10pm.
If she took that flight yesterday, she is somewhere in town today.
If she took that flight yesterday, we'll see her tomorrow.
A condition clause (protasis) in the present tense refers to a future event, a current event which may be true or untrue, or an event which could be verified in the future. The result can be in the past, present, or future:
If it's raining here now, then it was raining on the West Coast this morning.
If it's raining now, then your laundry is getting wet.
If it's raining now, there will be mushrooms to pick next week.
If it rains this afternoon, then yesterday's weather forecast was wrong.
If it rains this afternoon, your garden party is doomed.
If it rains this afternoon, everybody will stay home.
Certain modal auxiliary verbs (mainly will, may, might, and could) are not usually used in the condition clause (protasis) in English:
*If it will rain this afternoon, …
*If it may have rained yesterday, …
Counterfactual
In these constructions, the condition clause expresses a condition that is known to be false, or presented as unlikely. The result clause contains a conditional verb form consisting ofwould (or could, should, might) plus a main verb in the base form (infinitive without to).
The contrary-to-fact present conditional, often referred to as the "second conditional" or "conditional 2", is used to refer to a current state or event that is known to be false or improbable. The past subjunctive (or in colloquial English, simply the past tense) must be used:
If she were [colloq. was] at work today, she would know how to deal with this client.
If I were [colloq. was] the king, I could have you thrown in the dungeon.
The same structure can be used to refer to a future state or event:
If I won the lottery, I would buy a car.
If he said that to me, I would run away.
In many cases, when referring to future events, the difference between a realis and irrealis conditional is very slight:
(realis) If you leave now, you can still catch your train.
(irrealis) If you left now, you could still catch your train.
The contrary-to-fact past conditional (sometime referred to as the "third" conditional, conditional 3) is used to refer to contrary-to-fact past events. The pluperfect (or past perfect) is used in the condition clause.
If you had called me, I would have come.
If you had done your job properly, we wouldn't be in this mess now.
Some varieties of English regularly use would (often shortened to (I)'d) and would have (often shortened to (I)'d have) in counterfactual condition clauses, but this is often considered non-standard: If you'd leave now, you'd be on time. (conditional 2.) / If you (would)'ve told me, we could've done something about it. (conditional 3.) Such use of would is widespread especially in spoken US English in all sectors of society, but these forms are not usually used in more formal writing. Nevertheless, some reliable sources simply label this usage as acceptable US English and no longer label it as colloquial.
Should can appear in the condition clause to refer to a future event presented as possible, but unlikely, undesirable, or otherwise "remote": If I should die before I wake, …, If you should ever find yourself in such a situation, …


Unduh:
http://en.wikipedia.org/wiki/Conditional_sentence
http://www.ego4u.com/en/cram-up/grammar/conditional-sentences