The independent clauses of a compound sentence joined asyndetically are divided by a comma to denote a brief pause, falling tone, and often enumeration of closely connected actions. The copulative conjunction ‘and’ might be inserted between the clauses: “One hand went to the heart, the other outstretched toward the flag”.
In case of a longer pause and weaker connection, to denote enumeration of actions, the independent clauses of a compound sentence joined asyndetically are divided by a semicolon, especially if there is a comma, or commas, within these clauses: “The doors of the small sitting-room, bedroom, kitchen and bathroom were open; the walls were distempered apple-green, the floors covered with dark-green linoleum”.
The second or third independent clause of a compound sentence may have an adversative meaning. Such clause is introduced by a comma; in case of a longer pause, by a semicolon. The adversative conjunction ‘but’ might be inserted between the clauses. For example: “He has looked at me with those eyes of his. They do not love; they threaten; they are savage as a wild tiger’s”.
The second or third independent clause of a compound sentence joined asyndetically may have a causal meaning. Such clause is mostly introduced by a colon or a dash, sometimes by a comma. The causal conjunction ‘for’ might be inserted between the clauses: “No one replied: they had probably not understood”.
There is usually a comma before the dash.
The second or third independent clause of a compound sentence joined asyndetically may have a resultative meaning, and it is introduced by a comma or a semicolon. The resultative conjunction ‘so’ might be inserted between the clauses: “The door was open; sounds came from the kitchen”.
When the second or third independent clause of a compound sentence has an explanatory meaning, it is introduced by a colon or a semicolon: “But think: we could have whole columns of newspapers devoted to us for days”.
Both parts of a disjunctive question, being independent clauses of a compound sentence joined asyndetically, are divided by a comma to denote falling tone, connection of meaning, and a short pause: “You can do that, can’t you?”
Sometimes there is a dash between the clauses to denote a longer pause: “You didn’t throw away any cocoa last time you were here – did you?”
The independent clauses of a compound sentence joined by coordinative conjunctions or adverbs are usually separated by a comma (or commas) to denote a short pause; by a semicolon, in cases where a full-stop might be put if the conjunction were omitted, to denote a longer pause and weaker connection. There is also a semicolon if there are commas within the independent clauses: “The loud pitch of John’s voice got on his nerves, besides he could feel a draught round his legs”. (copulative co-ordination); “On my rising in the morning my preparations were soon made; or, rather, there were practically no preparations to make”. (disjunctive co-ordination); “Babbit did not care to be seen talking with such a fanatic, but in all the Pullmans he could find no other acquaintance”. (adversative co-ordination); “Few people were about, for it was really cold”. “They were tardy in recognizing this, for not one of the Junta liked him”. (causal co-ordination)
In compound sentences before ‘and’, ‘but’, ‘or’ the comma may be omitted to denote close connection: “By nine o’clock of that evening snow lay deep in the streets and the weather had become bitter cold”.
In case of several independent clauses, when the coordinative conjunction is repeated, there is a comma before each conjunction: “The Hansons expected her to go home, and she wanted to get away, and yet she did not want to go home”.
If a compound sentence contains several clauses enumerating closely connected actions, there are usually commas between the clauses, also before the conjunction introducing the final clause. In case of weaker connection, there is a semicolon between the independent clauses. For example: “The squire raised his gun, the rowing ceased, and we leaned over to the other side to keep the balance”.