As demonstrated by the following examples, a series is composed of three or more parallel elements, and the series can appear in the beginning, middle, or end of a sentence:
- Stretching, warming up, and cooling down are important to a good exercise program.
- All of the necessary qualities of a good assistant -- typing, shorthand, and patience -- she had in abundance.
- The three qualities of a good introduction are context, purpose, and organization.
Editors and grammarians are in sharp disagreement about whether a comma should be placed before the last element in a series. The trend in the popular press is not to include the comma if the elements in the series are brief. However, many well-known stylists have persuasively argued that conjunctions connect and commas separate, so it is incorrect in their opinion to judge the comma as redundant punctuation before a conjunction such as "and." In addition, uninformed readers may perceive the last two elements in the series to be a compound if the comma is omitted. For example, placement of the comma before the word "and" in the following example makes it clear that flowering plants are not the same as ornamental bushes:
- The landscaping contract includes several exotic plants, ornamental bushes, and flowering plants.
Occasionally, as dictated by your ear and the rhythm you hope to establish, you may want to insert a comma and forgo the and, as in this example:
- We have a government of the people, by the people, for the people.
When you want to slow down the rhythm of your sentence and emphasize a point, you can replace all the serial commas with and or or:
- If the abuse of the wetlands continues, we will be without waterfowl and fish and wildlife.
- He does not like shrimp or crayfish or lobster or anything that turns red when cooked.
When you must present a long array of parallel elements in your documents, you can avoid listing them by grouping them into logical parts and punctuating accordingly, as demonstrated by the following examples:
- Writing is painful and exhilarating, tedious and inspiring, chaotic and planned.
- Human activities such as coal and oil burning, population growth and increased food demands, clearing and burning forests have caused increases in the release of carbon dioxide and methane.
Finally, note that coequal, consecutive coordinate adjectives that modify the same noun should generally be separated with commas:
- Although he appears to have your best interests in mind, he truly is a competitive, combative, cantankerous boss.
However, you should not separate two consecutive adjectives with commas if the first adjective is modifying both the following adjective and noun as a unit, as illustrated below:
- The competitive track star runs forty miles a week.
Other comma resources:
- Use a Comma After Conjunctive Adverbs and Transitional Phrases at the Beginnings of Sentences
- Use Commas After Introductory Subordinate Clauses
- Use Commas Around Nonrestrictive Parenthetical Elements
- Use Commas Before Nonrestrictive Adverbial Phrases or Clauses at the Ends of Sentences
- Use Commas to Join Two or More Independent Clauses