What are the plurals of the following words?

1: Yes

2: No

Are they Yes's and No's?
Plurals and Apostrophes (From CCC)
We use an apostrophe to create plural forms in two limited situations: for pluralized letters of the alphabet and when we are trying to create the plural form of a word that refers to the word itself. Here we also should italicize this "word as word," but not the 's ending that belongs to it. Do not use the apostrophe+s to create the plural of acronyms (pronounceable abbreviations such as laser and IRA and URL*) and other abbreviations. (A possible exception to this last rule is an acronym that ends in "S": "We filed four NOS's in that folder.")
* Jeffrey got four A's on his last report card.
* Towanda learned very quickly to mind her p's and q's.
* You have fifteen and's in that last paragraph.
Notice that we do not use an apostrophe -s to create the plural of a word-in-itself. For instance, we would refer to the "ins and outs" of a mystery, the "yeses and nos" of a vote (NYPL Writer's Guide to Style and Usage), and we assume that Theodore Bernstein knew what he was talking about in his book Dos, Don'ts & Maybes of English Usage. We would also write "The shortstop made two spectacular outs in that inning." But when we refer to a word-as-a-word, we first italicize it - I pointed out the use of the word out in that sentence. - and if necessary, we pluralize it by adding the unitalicized apostrophe -s - "In his essay on prepositions, Jose used an astonishing three dozen out's." This practice is not universally followed, and in newspapers, you would find our example sentence written without italics or apostrophe: "You have fifteen ands in that last paragraph."
Some abbreviations have embedded plural forms, and there are often inconsistencies in creating the plurals of these words. The speed of an internal combustion engine is measured in "revolutions per minute" or rpm (lower case) and the efficiency of an automobile is reported in "miles per gallon" or mpg (no "-s" endings). On the other hand, baseball players love to accumulate "runs batted in," a statistic that is usually reported as RBIs (although it would not be terribly unusual to hear that someone got 100 RBI last year - and some baseball commentators will talk about "ribbies," too). Also, the U.S. military provides "meals ready to eat" and those rations are usually described as MREs (not MRE). When an abbreviation can be used to refer to a singular thing - a run batted in, a meal ready-to-eat, a prisoner of war - it's surely a good idea to form the plural by adding "s" to the abbreviation: RBIs, MREs, POWs. (Notice that no apostrophe is involved in the formation of these plurals. Whether abbreviations like these are formed with upper- or lower-case letters is a matter of great mystery; only your dictionary editor knows for sure.)
Notice, furthermore, that we do not use an apostrophe to create plurals in the following:
* The 1890s in Europe are widely regarded as years of social decadence.
* I have prepared 1099s for the entire staff.
* Rosa and her brother have identical IQs, and they both have PhDs from Harvard.
* She has over 400 URLs* in her bookmark file.
Marius HancuNever form a plural with 's. That's non-standard.
Hi Marius

There is a grammatical school that accepts 's as an optional plural ending when the plural s is added to something other than a word:
in the 1990's / in the 1990s
They are MP's / MPs.

The apostrophe used to be quite common at least in BrE when I was young (in the early 17th century Emotion: smile) but has rapidly declined in popularity, I suppose with the British tendency not to use even commas and periods as much as is customary in AmE. I don't writein the 1990's myself but I live up to my signature: if anyone wants to use the apostrophe, let them.

Naturally I respect your opinion as well.

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Anonymous" "Six yeses and two noes so far."
Yesses and noes seems more cumbersome and less understandable than yes's and no's.

The goal for usage should be communication rather than correct 'rule following'.
1 2 3
Never form a plural with 's. That's non-standard.

yesses, yeses
nos, noes
 Cool Breeze's reply was promoted to an answer.
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in the 1990's / in the 1990s
They are MP's / MPs.
I agree. Both versions are acceptable. I don't think anyone will say that you are wrong if you use the version with the apostrophe.
Some things just need the apotrophe. Look, I got all As on my report card! (How odd does THAT look?) Look, I got all A's on my report card!

The difference, as you say, is whether what you are making plural is a WORD. I can't think of any time you would make a word plural with an apostrophe.
Jackson6612What are the plurals of the following words?

1: Yes

2: No

Are they Yes's and No's?

Does that mean my suggestions Yes's and No's are wrong?
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Jackson6612Does that mean my suggestions Yes's and No's are wrong?

yes noun [C] ... "Have you had any replies yet?" "Six yeses and two noes so far."

(http://dictionary.cambridge.org/define.asp?key=91991&dict=CALD )
Jackson6612Does that mean my suggestions Yes's and No's are wrong?
According to M-W dictionary yes.
Hi everyone,
something more interesting would be...

I'm an Italian cat and I live in a box in a house in Italy, which is in Europe.

How many ins/in's are there in that sentence? There are four ins/in's.

I know you are a dog, but you can't chase a cat just because it's a cat and every cat has to be chased by a dog.

How many cat's/cats are there in that sentence? There are three cat's/cats.

Thre is probably no right answer to this question... the answer could be "People write those things the way they like them best... Right? Emotion: smile
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