规则5 不要用逗号连接独立子句[rule-5]

如果两个或更多语法上完整、且未由连词连接的子句要构成一个复合句，恰当的标点符号是分号。

• 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，把这两句各写成两个句子、用句号代替分号，也同样正确。

Mary Shelley's works are entertaining. They are full of engaging ideas. It is nearly half past five. We cannot reach town before dark.

如果插入一个连词，恰当的标点就是逗号。（见规则4。）

• Mary Shelley's works are entertaining, for they are full of engaging ideas.
• It is nearly half past five, and we cannot reach town before dark.

把上面给出的三种形式比较一下，就能清楚看出第一种的优点。至少在上面这些例子里，它比第二种好，因为它以第二种形式根本不去尝试的方式，暗示了两个陈述之间的紧密关系；它也比第三种好，因为它更简短，因而更有力。的确，这种标明陈述之间关系的简单方法，是组篇中最有用的手段之一。如上所示，这种关系通常是因果关系。

注意，如果第二个子句前面是一个副词，例如accordingly、besides、then、therefore或thus，而不是一个连词，那么仍然需要使用分号。

I had never been in the place before; besides, it was dark as a tomb.

分号规则有一个例外值得在此一提。当子句很短且形式相似，或者句子的语气轻松随意、像在交谈时，逗号更可取。

• Man proposes, God disposes.
• The gates swung apart, the bridge fell, the portcullis was drawn up.
• I hardly knew him, he was so changed.
• Here today, gone tomorrow.