If the parenthetical expression is long and not very closely related to the rest of the sentence, dashes or marks of parenthesis are frequently used.  Some writers use them even when the connection is somewhat close.

5.  The comma is frequently used to separate the parts of a long compound predicate.

  Pine torches have no glass to break, and are within the reach of any man
    who can wield an ax.

6.  A comma is often used to separate a subject with several modifiers, or with a long modifier, from the predicate verb.

One of the mistakes often made in beginning the study of birds with small children, is in placing stress upon learning by sight and name as many species of birds as possible.

7.  Participial and adjective phrases and adverb phrases out of their natural order should be separated from the rest of the sentence by commas.

  A knight, clad in armor, was the most conspicuous figure of all.

  To the mind of the writer, this explanation has much to commend it.

8.  When negative expressions are used in order to show a contrast, they are set off by commas.

  They believed in men, not in mere workers in the great human workshop.

9.  Commas are used in complex sentences to separate the dependent clause from the rest of the sentence.

  The great majority of people would be better off, if they had more money
    and spent it.

  While the flour is being made, samples are sent every hour to the
    testing department.

If the connection is close, the comma is usually omitted, especially when the dependent clause comes last.

  I will be there when the train arrives.

10.  When a relative clause furnishes an additional thought, it should be separated from the rest of the sentence by a comma.

  Hiram Watts, who has been living in New York for six years, has just
    returned to England.

If the relative clause is restrictive, that is, if it restricts or limits the meaning of the antecedent, the comma is unnecessary.

  This is the best article that he ever wrote.

11.  Commas are used to separate the members of a compound sentence when they are short or closely connected.

  Ireland is rich in minerals, yet there is but little mining done there.

    Breathe it, exult in it,
    All the day long,
    Glide in it, leap in it,
    Thrill it with song.

12.  Short quotations should be separated from the rest of the sentence by a comma.

  “There must be a beaver dam here,” he called.

13.  The omissions of important words in a sentence should be indicated by commas.

  If you can, come to-morrow; if not, come next week.

+6.  Rules for the Use of the Semicolon.+—­1.  When the members of a compound sentence are long or are not closely connected, semicolons should be used to separate them.