Day 2: Place a comma before a conjunction that joins two independent clauses.

The term independent clause refers to a complete sentence, whether it stands alone or is part of a longer sentence. It has a grammatical subject and a main verb, at a minimum.

Consider the sentence,

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“Tom loves Julie, and Julie loves Frank.”

This has two independent clauses. The first is “Tom loves Julie,” and the second is “Julie loves Frank.” The two clauses are joined by “and,” so you need a comma before the “and.”

Whenever you join two independent clauses by a conjunction (and, but, or, yet, so, for, nor), put a comma in front of the conjunction. Now consider this sentence:

“Mary winked at me, and Bob sighed.”

If you leave out the comma before “and,” the reader will have to decide whether Mary winked at only me or if she winked at me and Bob. Only when the reader gets to “sighed” will he or she realize that Mary is winking at me and that Bob is the person sighing. This makes the sentence confusing, and the reader may have to re-read it to understand its meaning. That comma makes the sentence clear.