Introductory and Compound Commas

The correct use of these two comma rules rests on your ability to recognize where your main clauses begin and end. To correctly place the introductory comma, you must know where your introductory element ends and where your main clause begins. To correctly place the compound comma, you must know where you have finished with one main clause in and where you will begin the next.

It's worth noting that these comma rules rarely show up on standardized tests. In real life comma use varies so greatly among writers and publications that test makers cannot test a standard use. Nevertheless, we will adopt the rules below. These rules were chosen to aid in your learning the structure of sentences. You can see this at work in the first paragraph you read. The purpose of these two rules is to make you aware of your main clauses.

I. Commas with Introductory Elements

We often begin sentences with introductory elements because they help set readers straight before they get to our important point expressed in the main clause. One of the most common introductory elements is the adverb clause. Many of our sentences begin with these clauses that set a condition on the idea embodied in the main clause:

• When we went to the store, we found the shelves empty.
• After Desi had kissed Lucy, Fred kissed Ethel.
• Since the pool is closed, we will go to the beach.
• Because Harvey lost his wallet, he couldn't go to the movies.

Another common introductory element is the prepositional phrase. We don't bother with the following comma if we begin a sentence with only one prep phrase, but we do use the comma if we begin a sentence with two or more such phrases:

• Into the valley of death, rode the six hundred.
• Over the river and through the wood, to grandmother's house we go.
• Once upon a time in a galaxy far away, Luke Skywalker battled an evil empire.
• BUT NOT: At the play we saw our best friend perform.

• Barking loudly to attract attention, Lassie did her best to get Timmy help.
• Having been promoted to the rank of corporal, Jeff was eager to put his new stripes on.
• Broken beyond repair, the old lawnmower rusted in a dank corner of the garage.

II. Commas with Compound Sentences

This is one of those comma rules which - in real life - depend upon whether the sentence is clear or not. Many professional writers forego this comma, but since you're a student, you'd be well advised to put it in every sentence that demands it. The type of sentence you're looking for is one with two (or more) main clauses that are joined by a coordinating conjunction. "Coordinating" is a fancy word for "equal," and "conjunction" means "a word that joins." So coordinating conjunctions join grammatically equal words, phrases, or clauses. In this case, the conjunction is joining two main clauses: "Desi loves Lucy, and Fred loves Ethel." Without the comma a reader might easily think that Desi loves Lucy and Fred before she figures out that the sentence claims that two people each love different people. You're probably familiar with the common coordinating conjunctions: and, but, or, for, yet, so. If you find "so" in a sentence as part of the phrase "so that," the "so" isn't coordinating any more; it's subordinating: "He went to the store so that he wouldn't starve." The adverb clause beginning with "so that" sets a condition on the main clause. What if we put that clause at the start of the sentence? How would the sentence be punctuated?

It's often the case that when students learn this rule, they stick a comma in front of every "and," "or" or "but" they write. However, the comma-plus-conjunction combination is a signal to readers that a main clause follows. Therefore, reserving the comma only for two main clauses is important. Don't stick a comma between two words: "Fred liked bread, and cheese." Don't stick a comma between two phrases: "Fred liked eating bread, and throwing cheese." Don't stick a comma between two subordinate clauses: "Fred knew that bread was good for eating, and that cheese stuck to the wall when he threw it." All of the sample sentences confuse readers who are expecting a main clause after the comma-plus-conjunction combinations.

If you find yourself writing main clauses that have commas within them, you may find that putting a semicolon before the conjunction helps make clear that one main clause has ended and another is about to begin.

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