When in a compound sentence the clauses have each a different nominative, but have only one verb, expressed in the first clause and understood in the others, the ellipsis, or place of the verb, should be supplied by a comma.
Example:—A wise man seeks to shine in himself, a fool to outshine others.
A short quotation, or any expression that resembles a quotation, is separated by a comma from an introductory clause.
Example:—Dr. Thomas Brown truly says, “The benevolent spirit is as universal in its efforts as the miseries which are capable of being relieved.”
Dash —.—The dash denotes an abrupt break in a sentence.
Example:—Here lies the great—false marble, where?
Example:—Nothing but sordid dust lies here.
The dash is used to indicate that something is left unfinished.
Example:—We cannot hope to succeed unless—
Example:—But we must succeed.