unless是連詞,意為“如果不”、“除非”。例如:
One can’t learn a foreign language unless he studies hard. 不下苦功夫是學不好外語的。
I will not go unless I hear from him.
如果我不收到他的來信,我就不去。
[特別提醒] unless連接一個條件從句,等于if…not, 不同點在于:if …not是口語, unless為書面語,unless有否定意思。例如:
I shall go there unless it rains.
= I shall go there if it doesn’t rain.
我去,除非下雨(如果不下雨,我就去)。
但在下列情況下二者不能換用:
1)表示“由于未發(fā)生B而發(fā)生A”的句子只能用if…not, 而不用unless。例如:
I’d be glad if she doesn’t come this evening.
如果今天晚上她不來我將很高興。
2)if…not可以引導一個虛擬條件句,unless一般不引導虛擬條件句。例如:
If she weren’t so silly, she would understand.
如果她不那么傻,她就會明白了。
[跟蹤練習]
1. You won’t catch up with your classmates ____ you work harder.
A. and B. or
C. unlessD. if
2. The sports meet will continue ____ it rains this afternoon.
A. if B. since
C. as soon asD. unless
Key: 1.C 2.D