The Writing Center @ The University of Wisconsin - Madison

7. Omitted commas

Use commas to signal nonrestrictive or nonessential material, to prevent confusion, and to indicate relationships among ideas and sentence parts.

Incorrect:

When it comes to eating people differ in their tastes.

Correct:

When it comes to eating, people differ in their tastes.

Incorrect:

The Huns who were Mongolian invaded Gaul in 451.

Correct:

The Huns, who were Mongolian, invaded Gaul in 451.

["Who were Mongolian" adds information but does not change the core meaning of the sentence because Huns were a Mongolian people; this material is therefore nonrestrictive or nonessential.]

For more information on commas see Commas: Punctuating Restrictive and Non-restrictive Modifiers and Punctuating Coordinating Conjunctions and Sentence Adverbs, or take one of the free grammar, style, and punctuation workshops offered by the Writing Center.