"This morning I took out a comma.
This afternoon, I put it back in."
Comma's are kind of like table manners. I use them regularly and, I must confess, usually without too much thought. I guess I have some sort of innate faith in my ability to use them appropriately. And then an "expert" comes along and I think, wow, if I was put on the spot, I'm not sure I'd know every situation where that particular rule applies.
When I'm writing a blog or an email, I do toss commas around pretty recklessly. Kind of like dashes - love those...
But when I put on my editor hat, I get ruthless with commas. Whether my own writing or someone else's, if the comma isn't absolutely necessary, out it goes. Partly it's the markets I typically write in. In business or advertising or news-style writing, commas are fairly scarce. When spaces count as characters, those commas are a luxury. In more scholarly writings, the commas can be sprinkled throughout with a more generous hand. Of course, the sentences are usually longer so it could be argued that the commas take on more importance just to keep the right thoughts grouped together.
So when are they necessary? Well, it's often a matter for debate but here's a short list I like:
1. To separate the elements in a series
eg. Our traditional Christmas dinner includes turkey, ham, stuffing, and cranberry sauce.
Note: That last comma is sometimes called the Oxford comma and while appropriate is not necessary unless the last two items are likely to get muddled together without it. Personally, I kill it off every time I get the chance unless clarity really is an issue.
It was a hot, humid day on the bayou.
Note: A good rule of thumb to see whether the comma is necessary is to try replacing it with "and". It was a hot and humid day on the bayou is acceptable, but It's just a little and old bunny rabbit is not the way we would group those adjectives. We'd say (or we'd have our character say), "It's just a little ol' bunny rabbit."
2. To set apart parenthetical phrases or clauses (phrases that can be dropped from the sentence without it losing sense but that still expand or clarify part of the sentence)
eg. The twins, Ian and Igor, had a habit of breaking their grandmother's knickknacks.
3. After introductory phrases
eg. Leaving the boat on shore, Ellen trudged up the beach towards the dunes.
Note: The advisability of overusing this type of sentence in writing is an entirely separate issue...
4. To set a direct quote apart from the text
eg. "It's too bad we have to have winter," said Sandy.
Of course, if the quote is not a complete sentence, but just a phrase or snippet, there is no comma before the quote although the attribute (identifying the person who gave the quote) is often treated as a parenthetical phrase (see #2).
eg, The use of slug bait, says master gardener Eli Spade, is one of "debatable virtue."
5. In dates, titles or other typographical conventions
eg. June 14, 1992, set records for its unseasonable rainfall.
Randolph James, Jr, led the parade as grand marshal.
Walter Spivins, MD, led the research team at Ample Health Institute in Flatlands, GA.
6. To avoid confusion
Sometimes you just have to add it in to make sure the reader keeps the right thoughts connected or has a chance to take a breath. But remember that it's often better for clarity to just break these types of sentences into two or three shorter ones.
There are many, many other places where commas are used - sometimes appropriately and sometimes not. It may be a question of style or taste rather than grammatical accuracy. Just remember that those commas can be to your writing what salt is to your cooking - a little enhances, a lot is unpalatable.
Want to see how your commas measure up? Here's a Comma Quiz that compares your commas to the "experts". And they give reasons for their choices, which can be just as helpful as knowing the "rules".
Maybe I should blog about "quotes" next...