Use a dash to set off an abrupt break or interruption and to announce a long appositive or summary.

A colon may introduce a quotation that supports or contributes to the preceding clause.

Use a dash only when a more common mark of punctuation seems inadequate.

In these sentences, the clauses introduced by which when, and where are nonrestrictive; they do not limit or define, they merely add something.

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.

Place a comma before a conjunction introducing an independent clause.

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.

Note that if the second clause is preceded by an adverb, such as accordingly, besides, then, therefore, or thus, and not by a conjunction, the semicolon is still required.

Do not join independent clauses with a comma.