Why do we use a comma before "and"? [duplicate]

Should I put a comma before the last item in a list?

I would like crackers, cheese and some soda.
I would like crackers, cheese, and some soda.

Solution 1:

Using a comma before the last item in a list is known as the Oxford Comma, sometimes the Serial Comma. It is used before conjunctions in a list like this with three or more items. Its use is purely written style and optional. It is more common in America outside journalism, and much less common in other English speaking areas of the world. There are arguments for and against which usually come down to comprehension. Wikipedia quotes these ambiguities:

To my parents, Mother Teresa and the Pope.

To my parents, Mother Teresa, and the Pope.

Also on that wiki page you can find lots of links to certain style guides. Comma use is something of a grey area though, and everyone has his own style. Pick what reduces ambiguity.

Language log has an interesting article on how reading comprehension can be improved with comma use, including this type.

Solution 2:

Not using that comma can lead to factual errors, as in the apocryphal book foreplate:

• Dedicated to my parents, Ayn Rand and God.

Solution 3:

The highest-scoring answer to this question asserts that using the serial comma is "purely [a matter of] written style and [therefore] optional." To demonstrate that neither including serial commas nor omitting serial commas leads in all cases to ambiguity-free sentences, he cites a familiar pair of amusingly misinterpretable dedications:

1. To my parents, Ayn Rand and God.

2. To my mother, Ayn Rand, and God.

Arguably the writer of the first example may be referring to four personages (two parents, a mortal author, and a Deity) or to two (two parents, one of whom who happens to be a mortal author and the other of whom happens to be a Deity). Likewise, the writer of the second example might be referring to three personages (one parent, one mortal author, and one Deity) or to two (a parent who happens to be a mortal author, and a Deity). The inference we seem to be invited to draw from these examples is that you can't win under either system of punctuation, so objectively it doesn't matter which one you choose: The two systems are equally unsatisfactory and equally susceptible to confusion. I think that this implicit argument misrepresents the case to a significant extent.

It is certainly true that each system fails in one of the examples above. But in other situations, the serial-comma system has an undeniable advantage over a strict no-serial-comma system. This fact is obvious from the advice that The Associated Press Stylebook (2002) offers publications that follow its (usually no-serial-comma) style. As I noted a year ago in my answer to a post about Serial commas in quotations, AP makes two important exceptions to its normal no-serial-comma rule:

Put a comma before the concluding conjunction in a series, however, if an integral element of the series requires a conjunction: I had orange juice, toast, and ham and eggs for breakfast.

Use a comma also before the concluding conjunction in a complex series of phrases: The main points to consider are whether the athletes are skillful enough to compete, whether they have the stamina to endure the training, and whether they have the proper mental attitude.

Establishing these two exceptions amounts to temporarily adopting the serial comma system in two specific situations where a strict no-serial-comma rule might yield ambiguous or difficult-to-follow sentences and where the serial-comma system has no countervailing disadvantages.

In short, the strict serial-comma system runs into ambiguity problems with certain appositive constructions, while the strict no-serial-comma system runs into ambiguity problems with certain appositive constructions, with certain series that contain one or more integral elements requiring a conjunction (as AP puts it), and with series whose elements are sufficiently complex.

As for the appositive ambiguity that plagues both systems in connection with God and Ayn Rand, I think that reworking the sentence to avoid the problem usually makes more sense than suspending your normal rule for including or excluding serial commas. Under either system of comma use, you can remove any shadow of potential ambiguity—in the more common circumstance where God and Ayn Rand are not your parents—by reframing the dedication as follows:

1. To my parents, to Ayn Rand and to God.

2. To my mother, to Ayn Rand, and to God.

I once encountered the following biographical snippet intended for the close of a magazine article:

He currently lives with his wife, a ferret, and a cat who thinks she is a ferret.

Our house style was to use a serial comma, but the author's description of his familial complications suggested that he might be risking a change for the worse in his current living arrangements if his wife (the ferret) got wind of his characterization of her. Retaining the serial comma after ferret clearly wouldn't do, but omitting it wouldn't get us out of the woods either. After all, just as one might describe a person as "a genius and a madman who knows he is a genius," one might (foolishly) refer to one's spouse as "a ferret and a cat who thinks [he or she] is a ferret."

My solution to the problem was to rework the sentence to relieve the overmatched comma (and its stripped-out doppelganger) of the burden of clarifying the relations between the named parties:

He and his wife have two pets: a ferret and a cat who thinks she is a ferret.

Ultimately a writer's best weapon in the struggle against unwanted ambiguity is neither the serial comma nor the lack thereof, but the ability to rephrase to avoid trouble.

Solution 4:

The basic question here is about disambiguation. Does the comma give you information that you need in order to fully understand the sentence? If it does, you want to include it. If not, it's not necessary, although it can still be used. It's common in the United States, not so much in the U.K.

In addition to the examples itrekkie listed, you could also consider this:

"I leave all my worldly possessions to my nieces Sarah, Jane, and Carol." This sentence implies that each niece would receive 1/3 of the estate.

"I leave all my worldly possessions to my nieces Sarah, Jane and Carol." This sentence could be read to imply that Sarah gets 50% of the estate, while Jane and Carol each get 25%.

Solution 5:

Sometimes the serial comma is necessary to delineate the final two items in the list when the final item is a compound item (containing the word "and").

My favorite drinks are Long Island Iced Tea, Bloody Mary, vodka, and Jack and Coke.

...and:

My favorite drinks are Long Island Iced Tea, Bloody Mary, vodka and Jack and Coke.

I'm not sure if anyone really drinks a vodka+Jack+Coke, but it could happen!