課本中不會(huì)教你的[U]692　unless和if…not

692　unless和if…not

① unless是從屬連詞，為書面語(yǔ)，用于引導(dǎo)條件狀語(yǔ)從句，意為“除非，如果……不”。unless本身具有否定意義，因此所引導(dǎo)的從句謂語(yǔ)動(dòng)詞用肯定式，相當(dāng)于if…not，常可換用。unless從句常位于句尾，表示強(qiáng)調(diào)時(shí)位于句首。

Don't come unless I call you. 我不打電話你就不要來(lái)。

=Don't come if I don't call you.

Unless you work hard，you will fail. 除非你努力工作，不然你會(huì)失敗的。

= If you don't work hard，you will fail.

② unless只能引導(dǎo)真實(shí)條件句，用直陳語(yǔ)氣，不可用虛擬語(yǔ)氣；而if…not既可以引導(dǎo)真實(shí)條件句，也可以引導(dǎo)非真實(shí)條件句，用虛擬語(yǔ)氣。因此，當(dāng)if…not引導(dǎo)非真實(shí)條件句，謂語(yǔ)動(dòng)詞用虛擬語(yǔ)氣時(shí)，就不可換用unless從句。

She will come unless it rains. 如果不下雨，她就會(huì)來(lái)。（真實(shí)條件句）

=She will come if it doesn't rain.

如果你早來(lái)十分鐘，你就會(huì)趕上火車了。

If you had come ten minutes earlier，you would have caught the train.

（非真實(shí)條件句，虛擬語(yǔ)氣）

Unless you had come ten minutes earlier，you would have caught the train.

③ unless如果所引導(dǎo)從句的謂語(yǔ)動(dòng)詞是否定式，就不可轉(zhuǎn)換為if…not結(jié)構(gòu)。

這本詞典是值得買的，除非你沒(méi)有足夠的錢。

This dictionary is worth buying unless you don't have enough money.

This dictionary is worth buying if you don't have enough money.

④ 當(dāng)從句的動(dòng)作或情況不發(fā)生，主句的動(dòng)作或情況才可發(fā)生時(shí)，要用if…not，不可用unless。

We'll be surprised if he doesn't do it that way. 要是他不那樣做，我們倒會(huì)感到奇怪了。

⑤ unless和if…not引導(dǎo)的從句，要用一般現(xiàn)在時(shí)代替一般將來(lái)時(shí)。

除非明天下雨，不然我們將去度假。

We shall go on a holiday unless it rains tomorrow.

We shall go on a holiday if it doesn't rain tomorrow.

⑥ unless如果所引導(dǎo)從句的主語(yǔ)和主句的主語(yǔ)相同，謂語(yǔ)中又有be動(dòng)詞時(shí)，從句的主語(yǔ)和be動(dòng)詞可省去。

She won't come unless invited. 如果不邀請(qǐng)，她不會(huì)來(lái)。（省去she is）