The Elements of Style
Elementary?Rule?4. Place a comma before a conjunction introducing an independent clause???
e.g.?The early records of the city have disappeared, and the story of its first years can no longer be reconstructed.
When the subject is the same for both clauses and is expressed only once, a comma is useful if the connective is but. When the connective is and, the comma should be omitted if the relation between the two statements is close or immediate. （當(dāng)兩個(gè)句子具有相同的主語赂摆，如果以but連接弯洗，用逗號分隔；如果以and連接蒸走，則無需逗號）
e.g.?I have heard the arguments, but am still unconvinced.
He has had several years' experience and is thoroughly competent
Elementary?Rule?5. Do not join independent clauses with a comma.
If two or more clauses grammatically complete and not joined by a conjunction are to form?a single compound sentence, the proper mark of punctuation is a semicolon. (用分號分隔兩個(gè)缺乏連詞連接的相關(guān)性從句)
e.g. Mary Shelley's works are entertaining; they are full of engaging ideas.
也可以用句號（periods）連接兩個(gè)獨(dú)立的句子。
Mary Shelley's works are entertaining. They are full of engaging ideas.
如果存在連詞，則用逗號連接兩個(gè)句子：
Mary Shelley's works are entertaining, for they are full of engaging ideas.
如果是以副詞連接兩個(gè)句子草冈，仍然使用分號：
I had never been in the place before; besides, it was dark as a tomb.
An exception to the semicolon rule is worth noting here. A comma is preferable when the clauses are very short and alike in form, or when the tone of the sentence is easy and conversational. （當(dāng)兩個(gè)句子非常簡短，形式相似枷畏，或者隱含著相互的對話别厘，則可以用逗號連接。意味著兩個(gè)句子彼此非獨(dú)立）
e.g.?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.
