Tuesday, September 22, 2009

Commas in a [Complicated] Series

"This product was chosen because it offers a high thermal performance for its cost, the ability to act as a drainage plane, a sufficient performance as an insulating sheathing material, and a favorable demonstration of cold climate permeability characteristics."

At the basis of this sentence is the following meaning--here is a product that offers four benefits. These four benefits are listed as a series separated by commas. Each comma has an important purpose in the sentence. It tells the reader that one item in the list is ending and a new one is beginning. Basic grammar. However, there are two camps regarding the final comma in the list--the one before the word "and." The first camp says that a comma isn't needed before a conjunction, and the second says that a comma is needed before it. Whether or not you fall into either of these two camps, there are certain cases where a comma is important to ensure the clarity of the sentence, and a complicated series is one of these cases.

What do I mean by a complicated series? While there are different types of complicated series, the one is the example lists items that are composed of numerous words. Here's a recap of the items:
  • a high thermal performance for its cost
  • the ability to act as a drainage plane
  • a sufficient performance as an insulating sheathing material
  • a favorable demonstration of cold climate permeability characteristics

At 7-8 words each, the items are lengthy. Commas remind readers that they are seeing a list of items and that they can pause for breath between them. By leaving out the final comma, the writer robs the reader of these reminders. Take a look at the sentence again without the final comma:

"This product was chosen because it offers a high thermal performance for its cost, the ability to act as a drainage plane, a sufficient performance as an insulating sheathing material and a favorable demonstration of cold climate permeability characteristics."

See how the last two items in the list merge? Adding a comma before the conjunction requires little effort on the writer's end and can offer a big benefit on the reader's end--clarity.

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