The main structural uses of commas



1. Conjunctive use of semicolon and comma:

    A  semicolon  joins independent clauses;
a comma with a conjunction also joins independent clauses.

    A  semicolon  joins independent clauses, and
a comma with a conjunction also joins independent clauses.

    A  sentence that consists of a single clause
is not a compound sentence and requires no joining comma.


2. Parenthetical use of comma:

    A pair of commas is used (as in the next sentence) in place of
parentheses.

    A pair of commas is used, as in this sentence, to serve as
parentheses.

One end of the sentence may replace the matching comma (as in the
next sentence).

One end of the sentence may replace the matching comma, as in this
sentence.


3. Serial use of comma:

    Commas serve for compound sentences, parenthetical elements,
and series.

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``the dropping of the comma before ``and'' in a series seems to me
a surrender of clarity, giving ``red, white and blue'' the same
rhythm as ``tea, bread and butter'' or ``Chaplin, Laurel and
Hardy.''

        John Updike (New Yorker, December 23 & 30, 1996)