GrammarPhile Blog

Using Commas in Writing

Posted by Phil Jamieson   Feb 11, 2014 6:30:00 AM

Just this last week, we were asked about our use of commas in a document. So, here are some rules we follow and hope you will too.

MODIFIERS IN A SERIES: Parallel tracks

Use a comma to separate two or more adjectives that modify the same noun, but only when the adjectives represent qualities that are parallel to or independent of each other.

A closer look. To tell whether adjectives in a series are independent modifiers (and should be separated by commas), see what happens when you insert the word and between them. If the insertion produces gibberish, the adjectives need to act as a unit and should not be separated by a comma. If the phrase still makes sense with the and, use a comma.
  • The report offers a penetrating, accurate analysis of the tournament skiboat industry. (A comma is needed between penetrating and accurate because each adjective could act as an independent modifier. Test: ... a penetrating and accurate analysis ... makes sense.)
  • We held the slalom contest on the small clean lake next to the highway. (No comma is needed between small and clean because the two modifiers work in tandem to identify the lake. Test: ... the small and clean lake ... doesn't make sense.)


Base your decision to insert or omit commas before and after relative clauses on the extent to which the clause limits the meaning of the word it refers back to. Omit commas when the clause is restrictive, i.e., it limits the meaning. Insert commas when the clause is nonrestrictive, i.e., it doesn't limit the meaning.
  • People who live in glass houses shouldn't throw stones. (No commas are needed here because who live in glass houses is a restrictive clause. The sentence would not retain its intended meaning if the clause were left out.)
  • The people next door, who live in a glass house, have begun throwing stones. (Commas are needed here because who live in a glass house is nonrestrictive. It isn't necessary to identify who is meant by "the people next door.")

THE APPOSITIVE: Mirror image

Use commas to set off any word or words that are appositive to another word in the sentence.

A closer look. A word or group of words is in apposition to another word when it is, in effect, a mirror image of that word: when it is the same part of speech and relates to the rest of the sentence in the same way. The most common mistake people make with appositives is to use only one comma, rather than a set.
  • Bartholomew Smithens, the noted big-wave surfer, will [not Bartholomew Smithens, the noted big-wave surfer (no comma) will ...] be the guest speaker at next week's tea. (The phrase in italics is in apposition to the subject, Bartholomew Smithens.)
  • Alligator wrestling, a sport that originally developed in Florida, has begun to lose some of its appeal, especially among the alligators. (The clause in italics is in apposition to the subject, alligator wrestling.)

An even closer look. Don't confuse a true appositive with a noun preceded by a modifier.
  • Noted big-wave surfer Bart Smithens will be the guest speaker at next week's tea. (No comma is needed here because Noted big-wave surfer is a modifier, not an appositive.)

Source: Grammar for Smart People, by Barry Tarshis.

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