if和unless的用法讲解

If 和 unless引导的条件状语从句

我们用if引导的条件状语从句来讨论可能的条件以及该条件成立时可能的结果。一. 学习if引导的条件状语从句的用法，我们可先从如下的口诀入手： If条件句不一般，几个要点记心间； 条件句，放在前，逗号要句中间 条件句表可能，主句多用将来时； 条件句表事实，主句常用现在时。

We can walk thereif we can’t find a bus.如果我们找不到公车，也能走路去那里 主句条件状语从句

If it rains tomorrow, we will not go to the zoo.如果明天下雨，我们就不去动物园 条件状语从句主句

What will you goif you find someone in danger? 主句条件状语从句

如果你发现某人有危险，你会怎么做？ If 条件句有不同的类型，简述如下： 1. 用if条件句表达客观真理或普通现象

If条件句用于表达客观真理或普通现象时，主，从句时态均用一般现在时，如： Eg.If you freeze water, it turns into ice. A fish dies if you take it out of water. 2. 用if 条件句表示将来可能发生的事情

在表示将来可能发生的事情的if条件句中，主句用一般将来时，而if从句用一般现在时表示将来的时间，即主将从现

Eg.If I like the house, I will buy it. 如果我喜欢这房子，我就会把它买下 I will tell her if I see her. 如果我见到她，我就会告诉她。 主句中的will也可以用情态动词can, may 或might等代替。如：

Eg.If they are friendly，I might invite them to the party. 如果他们很友善，我可能会请他们去参加聚会

If we hurry now, we can stop for coffee later. 如果我们现在抓紧时间，就可以稍后去喝咖啡

1 / 4

注意：在条件句中，主句部分只能使用动词will的一般将来时，不能使用be going to的结构

二. Unless 的条件句

表示在特定条件下，才决定做或不做一件事，中文用的连接词一般是“除非”和“否则”。如：除非刮台风，否则演唱会将如期进行。在英语中，我们可以用unless表达这个意思，相当于if not。以这个句子为例： The concert will be held as schedule unless there is a typhoon. = the concert will be held as schedule if there is not a typhoon

She will keep on singing unless she is told to stop. 她会一直唱下去，除非有人叫她停止

= she will keep on singing if she is not told to stop 也可以用or(否则) 来做同义句转换

Unless you listen carefully, you won’t know the answer. = if you don’t listen carefully, you won’t know the answer. = you should listen carefully, or you won’t know the answer.

2 / 4

If&unless 区别练习

1. If I ________ his phone number, I will tell you.

A. find B. found C. will find D. have found 2. We will go camping if it _______ tomorrow.

A. Won’t rain B. didn’t rain C. doesn’t rain D. isn’t raining 3. I’m waiting for my friend. If he _______, I ______ swimming alone.

A. doesn’t come; will go B. won’t come; will go C.will come; won’t go D. don’t come; will go

4. ______ you go to the supermarket at 7 p.m, you can buy a lot of cheap food.

A. If B. Unless C. Whether D. When

5. I won’t get to the party on time ______ I catch the first train tomorrow morning.

A. If B. Unless C. Whether D. When 6. ------Shall we go on a picnic this weekend? ------Good idea! Unless it _______.

A. rains B. doesn’t rain C. rain D. won’t rain 7. -----Can I change the jacket for another one ______ it doesn’t fit me well? ----- Of course.

A. unless B. if C. that D. though 8. Nobody can learn maths well he works hard on it.

A if B unless C thought D however 9. If fish away from water, they die.

A are taking, won’t B are taken, will C are being taken, will D take, won’t

10. Each student can ask teachers for help if he how to work out the problem.

A will know B won’t know C don’t know D doesn’t know

3 / 4

诚信 笃行 勤奋 一 A用 if或unless填空 1. he wants to see me, you can tell him to wait. 2. it snows tomorrow, we’ll have a day or two off. 3. We won’t go to his party he invites us. 4. She is sure to pass the examination she is ill. 5. I’ll take that computer I have enough money. 6. my grandma wears glasses, she can see better. 7. I won’t buy that backpack it costs less than $20 8. I’m tired; I’ll have a rest for tea. 9. You won’t get paid for time off you have a doctor’s note. 10. you will get a toothache you do clean your teeth regularly. B 用所给单词的适当形式填空 1. If he (get) a low mark in the test, he (study) harder. 2. If you (swim) every day this summer, you (be) very healthy. 3. If he (not hurry), he (not see) the beginning of the match. 4. You can’t go out unless you (finish) your homework. 5. Unless I save my money carefully, I (not be) able to buy a football. 6. If it (not rain) tomorrow, we (go) to the park. 7. If he (return) to the school, I (let) you know. 8. He smoking unless he (have) enough money. 9. They can remember it better if someone (give) them some advice about it. 10. The man (set off) if he (buy) the air ticket. 二 解释句子 1. you will feel worse unless you take more rest. 2. you will be late for work if you don’t hurry up. 4 / 4

3. no one is going to help you unless you change your mind. 1 18926518344 83872250

本文来源：https://www.bwwdw.com/article/2rxd.html