Using Commas with Restrictive and Nonrestrictive Elements
This third and final article on the topic of commas in the Proper Punctuation series will teach you when you should use commas to separate additional information from the rest of the sentence and when you should not.
Do not use a comma to separate a restrictive element from the rest of the sentence
For our discussion, an element is a phrase which gives additional information about a noun or pronoun. If this element is required for the reader to fully understand what the writer means by the noun or pronoun, we say that the element is a restrictive element. You can tell that an element is restrictive when removing the element would drastically change the meaning of a sentence.
The underlined phrase in the sentence below is a restrictive element:
“Bananas which have not yet ripened should not be eaten.”
This underlined phrase is absolutely necessary for the reader to understand what is being said, and so it is a restrictive element. Without the phrase, the meaning of the sentence is very different:
“Bananas should not be eaten.”
The restrictive element used in this example restricts the reader’s imagination. The reader should picture a firm green banana instead of any banana they want to.
Putting a restrictive element within commas is incorrect. When a restrictive element is placed within commas, the commas indicate that the element is inherently true of the noun or pronoun. If you were to write the sentence below, you would be telling the reader that all bananas are not yet ripe, and this is why they should not be eaten:
“Bananas, which have not yet ripened, should not be eaten.”
Use a comma to separate a nonrestrictive element from the rest of the sentence
As opposed to a restrictive element, a nonrestrictive element gives additional information which is not essential to the reader’s understanding of a sentence. A nonrestrictive element could be lifted out of a sentence, and the reader would still get roughly the same message.
The underlined phrase in the sentence below is a nonrestrictive phrase:
“Bananas, which are high in potassium, are good to have with breakfast.”
Without the nonrestrictive element, a little bit of detail is lost, but the meaning of the sentence is not altered:
“Bananas are good to have with breakfast.”
The nonrestrictive phrase is not essential to the sentence’s meaning because it merely tells the reader something that is true of all bananas. It does not restrict the reader’s ability to imagine what kind of bananas are being discussed.
Omitting the commas which should surround a nonrestrictive clause is a mistake. If you were to write the sentence below, you would be telling the reader that not all bananas are high in potassium and that only the ones that are high in potassium are good to have with breakfast:
“Bananas which are high in potassium are good to have with breakfast.”
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