It is proper ... that ...
结构︰It is+意志形容词(important 等)+(that)+主词+(should)+原形动词
说明︰意志<形容词>包括 important，necessary，imperative，essential，urgent，desirable， advisable，recommendable，proper 等。that-<子句>中只能用<助动词> should，不可用 must，而 should 往往予以省略。
It is necessary that he (should) sort out the information for my reference.
他有必要整理些资料供我参考。
It is essential that he get up early. 他有必要早起。
It is urgent that food and clothing (should) be sent to the sufferers.
急需将食物和衣服送给灾民。
It is desirable that we (should) provide for the poor at Christmas.
在圣诞节施舍穷人是可喜的事。
It is important that he be quiet. 他该保持安静是有必要的。
It is important that he not do it. 他不该做那事是有必要的。
It is requested that all members be present at the party. 全体会员都被要求出席这次晚会。
It is proper that such a bad man be punished severely. 这么坏的人受重罚是应该的。
Imperative Sentence + Conj. + Main Clause
结构︰祈使句+连接词+主句
说明︰<祈使句>表示须具备的条件，主句表示可能的结果。<祈使句>代替 if 子句进行评说，提出要求，订立协议，提供建议或威胁等。<祈使句>的用法比 if 子句表示的更为紧迫。
Provide the materials and we’ll do the job. 提供材料，我们就做这活。
Stop shouting or you’ll wake up the neighbors. 不要喊了，否则你会把邻居吵醒的。
Put that down or else I’ll smack you. 把它放下，不然我就揍你。
Be there on time, otherwise you’ll create a bad impression.
要准时来，否则你会给人一个坏的印象。
Fail to pay and they’ll cut off the electricity. 你(如果)不付款，他们就要断电。
Stop eating sweets, or you won’t get any dinner. 你如果不停止吃糖，你就不要吃饭。
Unless ...
结构︰Unless+子句，主要子句
说明︰此句型意为“除非…”。unless 引导一个否定假设句，相当于 if ... not ...，有时可以互换使用。总体上看，unless 的语气强于 if ... not ...，而且有时较为常用，例如在最后通牒中。
Unless you change your mind (=If you don’t change you mind), I won’t be able to help you.
除非你改变你的想法，否则我不能帮助你。
Unless the management improves their offer, there’ll be a strike.
除非资方做出进一步的建议，否则将举行罢工。
I couldn’t have got to the meeting on time - unless I had caught an earlier train.
我不可能及时赶到会场，除非我赶上了较找的一班火车。
Provided/Providing (that) ....
结构︰Provided/provided(that)+子句，S+V ...
说明︰此句型意为“如果…”。Provided/Providing (that) 引导假设条件句，其功能相当于 if。
Provided/Providing (that) you clear your desk by this evening, you can have tomorrow off.
如果你到今晚把手头上的工作做完，你明天就可以休息。
As/So long as ...
结构︰As/So long as +子句，S+V ...
说明︰此句型意为“如果…，只要…”。As/So long as引导一个条件假设句，其功能相当于 if。
So (As) long as you clear your desk by this evening, you can have tomorrow leave.
如果你到今晚把手头上的工作做完，你明天就可以休息。
As long as you drive carefully, you will be very safe. 如果你开车小心，你就会很安全。
You may eat anything, so long as you don’t eat too much.
只要不吃得太多，你可以吃任何东西。
As long as live, I will help you. 只要我活着，我都会帮助你。
As long as you don’t betray me, I’ll do whatever you ask me to (do).
只要你不出卖我，要我做什么我都愿意。
We’ll ship the goods at an early time as long as there is a steamer.只要有船，我们就尽早装货。
You will never be good students so long as you goof around.
如果你们成天游手好闲，就永远也成不了好学生。
Suppose/Supposing (that) ...
结构︰Suppose/Supposing (that)+子句，S+V ...
说明︰此句型意为“如果…，假使…”。Suppose/Supposing (that) 引导假设条件句，其功能相当于 if。
Suppose/Supposing (that) we miss the train, what shall we do?
如果我们误了火车，我们将怎么办?
What if/Say ...
结构︰What if/Say+子句，S+V ...
说明︰此句型意为“假设…”。What if 和 Say 用来引导一个假设条件句，其义相当于 Let us suppose(让我们假设)。
What if/Say he goes home before us and can’t get in? What will he do then?
假设他在我们之前赶到家而又进不去呢?那他怎么办呢?
What if/Say you were to run out of money? What would you do?
假设你的钱用完了呢?你将怎么办呢?
With luck ...
结构︰With luck，+主要子句
说明︰With luck 为含蓄假设条件句(即不用 if 直接引导)。with luck 意为“如果幸运的话，如果运气好的话”。
With luck, we’ll be there by tomorrow.幸运的话，我们明天将到达那儿。(=If we are lucky)
With luck, she will get the job. 如果幸运的话，她将得到那份工作。(=If she is lucky)
Given time ...
结构︰Given time，+主要子句
说明︰此为含蓄假设条件句(即不用 if 直接引导)。Given time 意为“(如果)给以时间的话”。
Given time, they will probably agree.给以时间的话，他们可能会同意。(=If they are given time/If we give them time)
To hear him talk, ...
结构︰To hear him talk，+主要子句
说明︰此句型意为“听某人谈话(的口气)…”。从形式上看，To hear him talk 似为不定式词组，但实则为含蓄条件句(即不用 if 直接引导)。To hear him talk 相当于 If you could hear him talk。
To hear him talk, you’d think he was Prime Minister.
听他谈话(那口气)，你会以为他是首相呢。
To hear you talk, I’d think you were Prime Minister.
听你谈话(那口气)，我还以为你是首相呢。
Without ..., S + V ...
结构︰Without …，+主要子句
说明︰此句型意为“如果没有…”，是导致主要子句结果发生的必要条件。Without ... 为含蓄假设条件句，此用法在口语表达中最为常见。without 意为“(如果)没有…的话”。Without 既可以放在句首，也可以放在句尾，放在句首有强调作用。此外，如果主要子句用否定式，则和 without 构成双重否定，表示特别强调 without 之后项为主要子句动作发生之必备条件。
Without your help, I couldn’t have done it.
(如果)没有你的帮助，我是不会做成的。(=If you hadn’t helped me)
She can’t solve the problem without his help.如果)没有他的帮助，她不可能解决这道题。
We can’t live without air or water.(如果)没有空气或水，我们就无法生存。
Fish cannot live without water.(如果)没有水，鱼儿就无法生存。
责任编辑：八月骄阳
