Completing Sentences Containing Coordination

When to Use a Comma and When to Avoid One

Instructions: Choose all endings that will fit onto the beginning. This means that you must take care to notice what kind of structure is promised by the sentence structure and the punctuation or lack thereof. In some cases there are more than one correct answer.

Punctuation with Coordinate Conjunctions

      Since the voice has many subtle ways of making meaning clear, speakers sometimes add or omit pauses without causing confusion. Writers, though, use commas to recommend a pause for clarity. If we understand why pauses in certain places help people understand us better, we can make sensible use of commas.
      When we join ideas with and, but, and or, we put a comma before the conjunction in two situations: when the next sentence element is a self-contained proposition having its own subject and predicate (this is called an independent clause) and when the next sentence element is the last item in a list (that is, a series of three or more parallel items). Aside from these two situations, there is only one other possibility: the conjunction stands between two parts of a sentence, such as two subjects or two adjectives, or two predicates. When we come to what looks like the end of a sentence and see an and, we like to know whether we can swallow what we are chewing now before taking another bite or whether some extra tidbit is to be added first. Consider this incomplete sentence:

      The dragon's claw explored the crevice daintily but

The lack of a comma tells a reader that the sentence will go on to describe the manner of exploring or else some other detail about the claw. The reader's voice will therefore not drop very far on "daintily, " since the claw's activity is not quite complete.

      The dragon's claw explored the crevice daintily but thoroughly.
      The dragon's claw explored the crevice daintily but left scratches in the rock that proved his strength.

On the other hand, just put a comma before "but" and down falls the voice on "daintily," and the reader and listener are both ready for a surprise—no more about the claw; rather, some other, yet unknown, agency will be at work. Will it mean rescue? Will it mean death? The comma means that we have only one certainty: that the claw is to be mentioned no longer in this sentence:

      The dragon's claw explored the crevice daintily, but his hot breath whipped through the opening and seared the cowering refugees' faces.
      The dragon's claw explored the crevice daintily, but just then a rumbling shook the cavern and let the daylight stream in.

      Sometimes the presence or absence of a comma (with the corresponding pause or lilt in the voice) signals an even more radical difference in meaning. After a comma, for is a conjunction giving a reason (much like because or since though a little more dramatic), but without the comma for is nothing but a preposition, as in "to do a service for someone." Likewise, without a comma but can sometimes be just a preposition, meaning except, as in "Everyone but Jim was out of step."