对于学术研究者，写作是攸关职业生涯的大事。自己对于写作并无所长，遂决开辟新专栏放置与“写作”相关的笔记，算是自我督促。
规则1：在三个或三个以上项目并列时，在最后一项前使用连词，其余各项用逗号隔开。
- red, white and blue
- gold, silver or copper
- He opened the letter, read it, and made a note of its contents.
这类逗号通常被称作并列逗号。
规则2：将插入语放在两个逗号之间。
1.短语
- Uncle Bert, being slightly deaf, moved forward.
2.用作称呼的名字或头衔
- Well, Susan, this is a fine mess you are in.
- Rachel Simonds, Attorney
需要注意：名词和表示其身份的限制性成分间不能用逗号隔开。
- The poet Sappho
- The novelist of Jane Austen
3.缩写
- Letters, packages, etc., should go there.
- Horace Fulsome, Ph.D., presided.
4.非限制性从句
非限制性从句是一种不定义或不限制先行名词的从句，只是单纯增添一些内容，应被视作插入语。
- The best way to see a country, unless you are pressed for time, is to travel on foot.
- The audience, which had at first been indifferent, became more and more interested.
- In 1769, when Napoleon was born, Corsica had but recently been acquired by France.
- Nether Stowey, where Coleridge wrote The Rime of Ancient Mariner, is a few miles from Bridgewater.
当然上述的例句都可以被拆分为独立的陈述句，比如：
- The audience was at first been indifferent. Later they became more and more interested.
与之相应的是限制性从句不可使用逗号隔开。
- People who live in glass houses shouldn't throw stones.
5.主句前的短语或从句
- Partly by hard fighting, partly by diplomatic skills, they enlarged their dominions to the east and rose to royal rank with the possession of Sicily.
规则3：在引导独立分句的连词前添加逗号
分句可以分为两类，一是独立分句，二是从属分句，也即从句。如果句子由两个分句组成，且第二个分句是由but, so, as, for, or, nor, while等连词引导时，需要在连词前添加逗号。
- The early records of the city have disappeared, so the story of its first years can no longer be constructed.
- The situation is perilous, but there is still one chance of escape.
当然，也有例外的情况。如果一个从句或一个需要用逗号隔开的引导性短语位于第二个独立分句前，则连词后不需要用逗号隔开。
- The situation is perilous, but if we are prepared to act promptly there is still one chance of escape.
此外，当两个分句的主语相同，而且主语仅出现一次时，如果连词是but，需要添加逗号；如果连词是and且两句关系紧密，就不需要添加逗号。
- I've heard the argument, but am still unconvinced.
- He has several years' experience and is thoroughly competent.
规则4：勿用逗号连接独立分句
两个或两个以上语法结构完整的句子在没有连词连接的情况下组成复合句时，用分号连接。
- Mary Shelley's works are entertaining; they are full of engaging ideas.
- It is nearly half past five; we cannot reach town before dark.
当然，将两个分句写成两个独立的句子，用句号分开也是正确的。
- Mary Shelley's works are entertaining. They are full of engaging ideas.
如果两句间有连词，则应遵循规则三，使用逗号更为合适。
- Mary Shelley's works are entertaining for they are full of engaging ideas.
对比以上三种形式，第一种的优势最为明显。和第二种相比，更能体现两个分句间的紧密联系；和第三种相比，更简明有力。因此，使用第一种形式表现两句间的关系是最有效的写作技法之一。
需要注意的是，如果第二个分句是由副词而非连词引导，如accordingly, besides, then, therefore, thus则仍需要使用分号。
- I had never been in the place before; besides, it was as dark as a tomb.
此外，如果分句短小且形式相近，或者句子语气轻松、口语化，则应使用逗号。
- Man proposes, God disposes.
规则5：勿将句子一分为二
该条规则强调的是该使用逗号不要用句号，比如下面句子的句号应该换成逗号。
- I met them on a Cunard liner many years ago. Coming home from Liverpool to New York.
如果作者使用了强调性的单词或短语，此时可用句号分隔，但作者应保证强调的合理性。
- Again and again he called out. No replay.
参考资料：
《风格的要素》
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