规则3 用逗号隔开插入语[rule-3]

The best way to see a country, unless you are pressed for time, is to travel on foot.

这条规则难以运用；常常很难判断某个单词（例如however）或某个简短短语究竟是不是插入语。如果对句子连贯性的打断很轻微，逗号可以稳妥地省略。但无论打断是轻微还是显著，都绝不能只省略一个逗号而留下另一个。下面这类标点是站不住脚的：

  • Marjorie's husband, Colonel Nelson paid us a visit yesterday.
  • My brother you will be pleased to hear, is now in perfect health.

日期通常含有插入性的词语或数字。标点如下：

  • February to July, 1992
  • April 6, 1986
  • Wednesday, November 14, 1990

注意，在以下写法中通常省略逗号：

6 April 1988

最后这种写法是书写日期的绝佳方式；数字之间被一个单词隔开，因此能迅速看懂。

直接称呼中的名字或头衔是插入语。

  • If, Sir, you refuse, I cannot predict what will happen.
  • Well, Susan, this is a fine mess you are in.

缩写etc.、i.e.和e.g.、学位的缩写，以及跟在名字后面的头衔，都是插入语，应当相应地加标点。

  • Letters, packages, etc., should go here.
  • Horace Fulsome, Ph.D., presided.
  • Rachel Simonds, Attorney
  • The Reverend Harry Lang, S.J.

然而，逗号不应把名词与限制性的身份说明分开。

  • Billy the Kid
  • The novelist Jane Austen
  • William the Conqueror
  • The poet Sappho

尽管Junior及其缩写Jr.通常被视为插入语，但逻辑表明它实际上是限制性的，因此不需要逗号。

James Wright Jr.

非限制性关系从句是插入语，由表示时间或地点的连词引导的类似从句也是如此。因此需要用逗号。非限制性从句是指不用于识别或限定先行词名词的从句。

  • 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 the Ancient Mariner, is a few miles from Bridgewater.

在这些句子中，由which、when和where引导的从句是非限制性的；它们不限定也不定义，只是增添一些内容。在第一个例子中，由which引导的从句并不用于说明几个可能的听众中指的是哪一个；读者想必已经知道。这个从句以插入的方式，补充了主句所陈述的内容。这三个句子中的每一个，都是两个本可以独立陈述的句子的组合。

  • The audience was at first indifferent. Later it became more and more interested.
  • Napoleon was born in 1769. At that time Corsica had but recently been acquired by France.
  • Coleridge wrote The Rime of the Ancient Mariner at Nether Stowey. Nether Stowey is a few miles from Bridgewater.

相反，限制性从句不是插入语，不用逗号隔开。因此：

People who live in glass houses shouldn't throw stones.

这里由who引导的从句确实用于说明指的是哪些人；这个句子与上面的句子不同，无法拆成两个独立陈述。同一条逗号使用原则也适用于分词短语和同位语。

  • People sitting in the rear couldn't hear, (restrictive)
  • Uncle Bert, being slightly deaf, moved forward, (non-restrictive)
  • My cousin Bob is a talented harpist, (restrictive)
  • Our oldest daughter, Mary, sings, (nonrestrictive)

当句子的主句前面有短语或从属子句时，用逗号把这些成分隔开。

Partly by hard fighting, partly by diplomatic skill, they enlarged their dominions to the east and rose to royal rank with the possession of Sicily.