When one of two clauses depends on the other, they are separated by a comma.
Example:—If you would be revenged on your enemies, let your life be blameless.
Two correlative expressions united by the conjunction as or than are written without a point between them.
Example:—Men are never so easily deceived as when they plot to deceive others.
But when united by any other word than one of these conjunctions, the correlative expressions are separated by a comma.
Example:—Though learned and methodical, yet the teacher was not a pedant.
Words or phrases in the same construction, forming a series, are separated from each other by commas.
Example:—Scrooge was his sole executor, his sole administrator, his sole assign, his sole residuary legatee, his sole friend, and sole mourner.—Dickens.
But when the members of the series are closely connected in sense, the commas should be omitted.
Example:—Government of the people by the people for the people.