I was taught in junior high school English classes that, when listing three or more items in a sentence, you do not place a comma before the final conjuntion. To wit:
In my sack I have apples, oranges and peaches.
Lately, however, I’ve been seeing it done (specifically, in my Dungeons & Dragons rulebooks) with a comma:
In my sack I have apples, oranges, and peaches.
Is one way more correct than the other? Has there been a change in the relevant grammar rule in the 26 years since my 8th grade English class? Is it simply a matter of which stylebook the publisher uses? Or is it context that matters - prose vs. technical writing?
A comma before the conjunction just seems extraneous, unnecessary and redundant to me.
That final comma is called the “Serial Comma.” Google it for arguments on both sides of the holy war.
I’m going to claim that it’s currently in vogue, as you’ve noticed, and I usually put it in. This is in the US; punctuation rules are different (sometimes very different) in other English-speaking countries.
As long as you’re consistent, you’ll be OK either way. (Or rather, you’ll get the same number of people insisting that you’re wrong either way).
I always include it because I think it makes things more clear. This is, however, one of those many grammatical issues where there’s not really a clear right or wrong answer.
You can make a list of things like: “She had in her bag oranges and apples, pears and plums, seaweed and salt.” Comma placement affects both how the words are semantically connected and the flow of the sentence.
If you split the items like this: “She had in her bag oranges, apples, pears, plums, seaweed and salt,” all of the items except the last two seem to be listed as separate while the last two are perceived as a unit.
Depending on how I intend the items in a list to be parsed, I use different styles. If I say, “Oranges, apples, pears and plums, seaweed and salt,” I want readers to see the phrases “pears and plums” and “seaweed and salt” as semantic units. If I intended them to be split up, I would have used a comma. To me, not including a comma before the “and” makes that part into a phrase instead of two separate items.
Then again, I usually use language pretty deliberately and often consider how different wording and punctuation affects the feeling of written language. YMMV.
This is not a grammar issue; this is a style issue. That’s why there can legitimately be an argument over this.
If you are required to follow a certain style, then you must use that. Personally, I use the serial comma whenever I can. It’s simply clearer and less prone to any possible ambiguity or misunderstanding.
Years ago on, IIRC, the old Dick Cavett show, Katharine Hepburn told a story about how an interviewer asked her about her leisure activities. Well, she said she liked both embroidery and target shooting. She also liked cats. The resulting story claimed that Ms. Hepburn liked “shooting cats and embroidery.” Ah, for the lack of a comma, she got a boatload of hate mail.
But if you want to “seaweed and salt” to be a unit, then you should say “She had in her bag oranges, apples, pears and plums, and seaweed and salt”, or the sentence is not parallel. It would be like saying “She had in her bags oranges, apples, salt.”
Depending on the effect you want, you can write a sentence that way since there are no hard and fast rules. As someone pointed out above, this is mostly a matter of style. If I’d wanted to put an “and” before the last item in the list, I would have. I left it off because it flows better without the extra “and.”
I always use the serial comma (makes me sound like a mass murderer), for all the reasons stated above, because it’s more logical, there’s no good reason for omitting it, and Barnes and Noble probably have several books that cover this issue. When I was overseas copy editing for an English language university press, one of the professors got back to me because I had inserted the commas. He said it was an American custom and he expected it the British way, but now I see he was wrong. America and Britain are each divided by a common comma.