There are three main types of commas that are commonly used, and frequently trip up an unwary writer: 1. In a list 2. Joining with a conjunction 3. Instead of brackets *Commas are NOT meant to be used “wherever you would pause”. Even if you’ve been told this in the past, it is not correct. There are specific rules for using commas , and they don’t include anything about pausing or taking a breath. 1. Commas in a list These are the commas we're most familiar with. Every item on the list is separated by a comma. I bought apples, oranges, grapes, and pears. 2. Commas used with a conjunction This type of comma joins two sentences together with a connecting word such as and, or, but, while, or yet. The comma is placed before the conjunction. We will go to the match, but Jack will go home early. 3. Commas used like brackets If an extra portion of a sentence could be placed in brackets it can be placed between commas instead. A way to test it is to read the sentence without the extra port...

There are only four specific uses for a comma according to R.L. Trask in his Guide to Punctuation : Listing, Joining, Gapping, and Bracketing. If the comma you want to use doesn't fit into any of those categories then the comma is the wrong choice of punctuation. This is my interpretation and summary of Trask's section on commas. Listing Commas These are the commas we're most familiar with. Apples, oranges, grapes, and pears The serial (or "Oxford") comma (the comma before "and") is not compulsory, but it does help to avoid ambiguity, such as in the infamous example: I'd like to thank my parents, Ayn Rand and God. It is only important to be consistent in your choice to use, or not use, the serial comma. If one of your sentences contains an ambiguity that requires a serial comma, you must edit every other sentence that contains a list where the serial comma has been omitted. Joining Commas A joining comma joins two sentences together w...