连字符是一种标点符号，具有多种功能。它可以形成复合形容词用于修饰名词，也可以将动词短语转化为一种名词，还可以将起修饰作用的几个词连在一起组成复合词。
连字符经常用于语法结构比较复杂或使用特殊术语的各种场合，例如文学作品、报纸、学术期刊、科研文章等。
需要注意的是，连字符不应与破折号（短划线）混淆。连字符的作用是把两个单词连接起来形成一个复合词，而破折号表示意思的转折或对上一句的解释。
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用于复合形容词的连字符
复合形容词的作用是通过两个词的组合来修饰一个名词，其作用就好像是单个形容词一样。只有当复合形容词用于名词之前时，复合形容词中才需要使用连字符。当复合形容词用于名词之后时，不使用连字符。
在名词之前使用带连字符的复合形容词
- Example
- The hyper-competitive nature of the financial industry has led to the proliferation of white-collar crime and the lack of well-intentioned financial advisors.
在名词之前使用不带连字符的复合形容词
当复合形容词中含有一个带“ly”的副词和一个形容词时，不能使用连字符。
- Incorrect
- One overly-saturated area of finance is debt consolidation, which targets mostly-young debt holders such as college students.
- Correct
- One overly saturated area of finance is debt consolidation, which targets mostly young debt holders such as college students.
在名词之后使用复合形容词时，不使用连字符
当复合形容词出现在名词之后时，无需使用连字符。
- Incorrect
- Plagiarism in online articles is becoming all-too-common.
- Correct
- Plagiarism in online articles is becoming all too common.
用于动词短语转化为名词结构的连字符
动词短语是一种复合动词，由一个主动词和跟随其后的至少一个副词或介词组成。动词短语用来表达一种动作时，无需使用连字符。但是，当动词短语转化为一个名词结构来使用时，应当使用连字符把两个或多个词连接起来使用，或不使用连字符而直接把两个词合并写成一个词使用。
| Phrasal verb used for action (not hyphenated) | Phrasal verb used as noun (hyphenated/single word) |
| The teacher had to boot up his computer. | The boot-up took longer than usual. |
| The dealer will bring in the chips to the game. | The poker player had to pay the bring-in. |
| The fund manager tried to break down the cash statement. | The trading floor listened to the daily breakdown on the news |
| The trader was not the only one to mix up the order. | The boss had to stay late to solve the mixup. |
用于前缀和后缀的连字符
英语中的几乎每个名词都可以在施加一个前缀后改变其含义，而关于在前缀与名词之间是否使用连字符，规定也不尽相同。
作为一条普遍经验，用于大写字母、数字和日期之前的前缀，需要使用连字符。
通常需要使用连字符的前缀例子
- Example
- Most anti-bacterial soaps are effective at killing germs.
- Example
- The self-service counter was very popular with customers.
- Example
- He hadn’t seen his ex-girlfriend in many years.
可以使用连字符的前缀例子
| Prefixes used without a hyphen | Prefixes used with a hyphen |
| The celebrity signed the autograph. | The student was on auto-pilot all day. |
| The scientist used the microscope. | The micro-scale model was too small. |
| The employee was proactive in finishing work. | The official was very pro-government. |
| The nonprofit organization helped sick children. | The foundation became non-profit after getting a grant. |
一贯必须使用连字符的前缀例子
- Example
- The Egyptian sculpture dated back to pre-1200 BC.
- Example
- The mid-December time period is hectic due to Christmas.
- Example
- The post-WWII period was one of great economic growth.
用于复合词的连字符
带连字符的复合词是由连字符连接的多个词组成。学生、科研工作者和工业界人士经常遇到大量带有连字符的技术词汇。其他常见的带有连字符的复合词见于表示层次结构中的排名或排序。
用于技术词汇的带有连字符的复合词例子
- Example
- The strength-to-weight ratio needs to be increased.
- Example
- The phase-contrast microscope will be delivered soon.
- Example
- The researcher used Python to analyze the time-dependent variable.
用于层次结构的带有连字符的复合词例子
- Example
- Her father-in-law did not appreciate her cooking.
- Example
- The editor-in-chief rejected the headline.
用于澄清含义的连字符
连字符还可以用于澄清含义，在某些情况下消除歧义。
| Hyphenated/Non-hyphenated terms | Meaning |
| The worker decided to resign her contract. | The worker did not renew her employment. |
| The worker decided to re-sign her contract. | The worker did renew her employment. |
| His wallet had twenty five dollar bills. | $100 total in bills. |
| His wallet had twenty-five dollar bills. | $25 total in bills. |
| He just saw a man eating chicken. | He saw a human male eating some chicken. |
| He just saw a man-eating chicken. | He saw a monstrous chicken that eats humans. |
连字符与破折号的区别
破折号（短划线）是表示意思转折的标点符号，它也可以用于表示对上一句进行补充解释说明的语句。
这句话的英文就没有表达清楚，最好加例子展示。