類型一： if + 形容詞 adj.

省略的主語和be，要注意主語和形容詞對應(yīng)。

• if true, this essay may change theory what we believed for a long time.
• Make a sign telling me if ready.

某些固定搭配：

• If necessary, ring me on my cellphone.
• If possible, let me know beforehand.

類型二：if + 過去分詞 past participle

和上一條基本一樣，這里就是把形容詞的位置換成了過去分詞，在高考英語中經(jīng)?？贾髦^一致的時候會在這里出考題，請注意主謂一致。

• I will say if asked.
• Small trifles can escalate to a violence event if not paid good attention to.
• This fact proves that if put in the same position, women are able to earn as much as men do.

類型三：if + 不定代詞 indefinite pronoun

這類省略比較依靠上下文，理解要靠語感。

• There are few people nowadays, if any, who remenber him.
• This seems to have little, if anything, to do with him.

類型四： if + 介詞短語 prepositional phrase

有些固定搭配，理解主要依靠語境。

• If in doubt, ask your doctor, he can give you further information.
• Their policies have changed little, if at all, since last election.
• If by any chance you can't manage dinner tonight, perhaps we can at least have a drink together.

類型五：if ever

常和seldom連用，表示極少，萬一，ever 后面可以接其他類型的成分（if ever 過去分詞/形容詞）

• He seldom sings if ever.
• I seldom do housework if ever.
• If ever you are in America, do give me a ring.
• The island is seldom if ever visited by ships.

類型六：if not/so

如果不/是

類型七：if need be

如果需要=if it is necessary