Comma or semicolon between independent clauses that have internal commas and that are joined by a coordinating conjunction

Question

In high school I learned that when joining two independent clauses where either contained a comma I should always use a semicolon before the coordinating conjunction. For example,

• If Alice had known then what she knew now, she never would have gone to the store; and Ignatz might still be alive.

or

• Alice, a girl of 12, went to the store; and Bill watched her leave from his window across the street.

However I've been told that this is an old-fashioned rule. What is more conventional in modern fiction? Should I be using a comma in these cases? If so, is there any case in which I should use a semicolon before a coordinating conjunction?

Answer 1

The semicolon is improperly used there if you wish to express the notion of coordination.

A semicolon establishes a new syntactic context; it is a divide across which coordination does not take place.

If Alice had known then what she knew now, she never would have gone to the store ^{no semicolon here} and Ignatz might still be alive.

The italicized clauses refer to two things both of which would not have happened had Alice known then what she knew now.

If you wish to express some doubt about Ignatz's death being a coordinated result, you might use a semicolon, or nowadays an em-dash:

If Alice had known then what she knew now, she never would have gone to the store — and Ignatz might still be alive.

I don't think the "rule" you were taught is old-fashioned, simply misguided. Can you find an example of this in the work of any major author?

Answer 2

It's not a "rule," it's just a matter of style. So, it's a guideline that can vary from one style guide to another.

It's also far from an old-fashioned guideline.

From The Chicago Manual of Style (17th ed.), 6.60:

When items in a series themselves contain internal punctuation, separating the items with semicolons can aid clarity. If ambiguity seems unlikely, commas may be used instead . . . Note that when a sentence continues beyond a series (as in the third example), no additional semicolon is required.

      The membership of the international commission was as follows: France, 4; Germany, 5; Great Britain, 1; Italy, 3; United States, 7.

      The defendant, in an attempt to mitigate his sentence, pleaded that he had recently, on doctor’s orders, gone off his medications; that his car—which, incidentally, he had won in the late 1970s on Let’s Make a Deal—had spontaneously caught fire; and that he had not eaten for several days.

      Marilynn, Sunita, and Jared, research assistants; Carlos, programming consultant; and Carol, audiovisual editor, provided support and prepared these materials for publication.

      but

      She decided to buy three watches—an atomic watch for travel within the United States, a solar-powered, water-resistant quartz for international travel, and an expensive self-winding model for special occasions.