Day 4: Elements of Style

Rule: "Place a comma before a conjunction introducing an independent clause."

As in: Laine gave a calculus test, and her students all cried.

In a two part sentence, where the second member is introduced by and, for, or, nor, or while will require commas before the conjunction. If, however, the two clauses have the same subject, and the subject is only included once, then more discretion is required. In the case that the conjunction is but, a comma is often useful. While, in the case that the conjunction is and, a comma should be omitted if the ideas in the clauses are similar. As in:

Laine's students wanted to do well, but did not.

Laine's students did not study enough and failed the test.

A final subtlety occurs when the second clause of our compound sentence is preceded by a dependent clause or introductory phrase that would be typically set off by commas. Here no comma is needed after the conjunction. As in:

"The situation is perilous, but if we are prepared to act quickly, there is still one chance of escape."