until he has come 強(qiáng)調(diào)直到.才 是一種臨界狀態(tài)
直到他回來我才完成作業(yè)
before he came 強(qiáng)調(diào)再他回來之前 我沒法完成作業(yè)
一、作為從屬連詞含義不同,引導(dǎo)從句性質(zhì)不同
unless與until均為從屬連詞,unless表“除非”,強(qiáng)調(diào)條件,引導(dǎo)條件狀語從句;until表“直到”,強(qiáng)調(diào)時間的延續(xù),引導(dǎo)時間狀語從句.
1.I didn't know the news until my teacher told it to me.
2.I couldn't know the news unless my teacher told it to me.
3.—Was his father very strict with him when he was at school?
—Yes.He had never praised him until he became one of the top students in his grade.
析:句1動詞didn't know表明該句強(qiáng)調(diào)時間的延續(xù),表“我不知道這消息”的狀態(tài)一直延續(xù)到“老師告訴我”,因此應(yīng)用until引導(dǎo)時間狀語從句.句2動詞couldn't know表明該句強(qiáng)調(diào)條件,表“我不可能知道這消息,除非老師告訴我”,因此應(yīng)用unless引導(dǎo)條件狀語從句.句3表明“他爸爸從來沒有表揚(yáng)他”的狀態(tài)一直延續(xù)到“他變成年級最好的學(xué)生之一”,因此也應(yīng)用until引導(dǎo)時間狀語從句.
二、作為從屬連詞引導(dǎo)的從句常用一般現(xiàn)在時表示將來
unless引導(dǎo)的條件狀語從句和until引導(dǎo)的時間狀語從句常用一般現(xiàn)在時表示將來.
例1:除非邀請你否則別進(jìn)來.
誤:Don't come in unless you will be invited to.
正:Don't come in unless you're invited to.
例2:除非他來,我們不可能去.
誤:Unless he will come,we won't be able to go.
正:Unless he comes,we won't be able to go.
三、作為從屬連詞引導(dǎo)的狀語從句可轉(zhuǎn)換為省略式創(chuàng)新句型
unless引導(dǎo)條件狀語從句和until引導(dǎo)時間狀語從句時,如果主從句主語一致(或主從句主語不一致,但從句主語為it),從句謂語部分含有be,可將從句主語和動詞be省略,構(gòu)成省略式創(chuàng)新句型.
例1:I won't come to see you unless I am asked to.除非你邀請我,我才會來看你.
析:因?yàn)橹鲝木渲髡Z一致,從句謂語又含有am,所以可將從句主語I和動詞am 省略,構(gòu)成省略式創(chuàng)新句型:I won't come to see you unless asked to.
例2:The soldiers will not cross the river unless they are ordered to.除非接到命令,戰(zhàn)士們不會過河.
析:因?yàn)橹鲝木渲髡Z一致,從句謂語又含有are,所以可將從句主語they和動詞are省略,構(gòu)成省略式創(chuàng)新句型:The soldiers will not cross the river unless ordered to.
注意:
until也可作為介詞.例如:
I have remembered her until now.直到現(xiàn)在我還記得她.是的