Different pattern of "if"

也請看看參考資料和意見欄的網址以看更多的例子。
Conditional Sentences / If-Clauses Type I, II and III
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. There are three types of Conditional Sentences.

Conditional Sentence Type 1→ It is possible and also very likely that the condition will be fulfilled.Form: if + Simple Present, will-FutureExample: If I find her address, I’ll send her an invitation.
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.


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.
ExceptionsSometimes Conditional Sentences Type I, II and III can also be used with other tenses.So far you have only learned the basic rules for Conditional Sentences. It depends on the context, however, which tense to use. So sometimes it's possible for example that in an IF Clause Type I another tense than Simple Present is used, e.g. Present Progressive or Present Perfect.

2014-01-13 21:16:00 補充：
http://www.weblearn.in/conditional_clauses/

2014-01-13 21:16:54 補充：
http://www.englisch-hilfen.de/en/grammar/if.htm

2014-01-13 21:17:00 補充：
http://www.kfmaas.de/gram_if.html

2014-01-14 09:33:40 補充：
Thanks Godfrey~

And more thanks here:
http://hk.knowledge.yahoo.com/question/question?qid=7014011200140

2014-01-15 02:59:23 補充：
感謝 Godfrey 的分享：

Besides conditionals,

"If" is used when making polite request.
I wonder if you could help me.
Would you mind if I open a window?

"If" is also used to introduce clauses.
I'm not so sure if I heard him correctly.

2014-01-15 02:59:36 補充：
"if" can be used as a noun.
There are too many ifs in your plan.

Zero conditional Type 0
If + present simple, .. present simple

2014-01-15 02:59:44 補充：
If I heat the ice, it melts.

2014-01-15 03:00:17 補充：
facts, habits

Besides conditionals,

"If" is used when making polite request.
I wonder if you could help me.
Would you mind if I open a window?

"If" is also used to introduce clauses.
I'm not so sure if I heard him correctly.

2014-01-14 08:35:50 補充：
"if" can be used as a noun.
There are too many ifs in your plan.

Zero conditional Type 0
If + present simple, .. present simple

If I heat the ice, it melts.

~ to talk about event that can occur at any time, and their results. (facts, habits, routine work, rule)