Coordinate clauses joined by copulative conjunctions.

Clauses joined by the conjunction and may be separated by a comma (if the connection between the clauses is close) or a semicolon (if the clauses are more independent). Occasionally a dash is used.

... a library was a most likely place for her, and he might see her there. (London)

He wondered what boat it was, and why she did not stop at the wharf — and then he dropped her out of his mind and put his attention upon his business. (Twain)

Coordinate clauses joined by the conjunctions neither; nor are generally separated by a semicolon.

Martin did not laugh; nor did he grit his teeth in anger. (Lon­don)

She would not listen, therefore, to her daughter's proposal of be­ing carried home; neither did the apothecary, who arrived about the same time, think it necessary. (Austen)

Occasionally a comma is found.

He could not bring them back, nor could he go back to them. (London)

But you can't get at him, neither can we. (Dickens)

Clauses joined by the conjunctive adverbs moreover; besides, then are usually separated by a semicolon.

He seemed to have no desire to go; besides his clothes were not good enough. (Cronin)

It was the custom of that youth on Saturdays, to roll up his shirt sleeves to his shoulders, and pervade all parts of the house in an apron of coarse green baize; moreover, he was more strongly tempted on Saturdays than on other days. (Dickens)

§ 9. Coordinate clauses joined by disjunctive conjunctions are usually separated by a comma. A dash may also be used.

The whole world had come alive again, was going as fast as we were, or rather we were going no faster than the rest of the world. (Wells)

Either his going had been again delayed, or he had yet procured no opportunity of seeing Miss Crawford alone, or he was too happy for letter-writing. (Austen)

Occasionally a semicolon or a dash is found before the conjunc­tion or.

But to live in ignorance on such a point was impossible; or, at least, it was impossible not to try for information. (Austen)

She was disappointed — or did it only seem to him? (Wells)