No matter how many times you learn possessive plural rules, you’re likely as not to forget that they even exist. It might be because you’re so used to not using the apostrophe, or so afraid of misusing it, that you often eschew the apostrophe altogether.
The rules for the possessive plural are, however, an important thing to learn. By learning when an apostrophe is used and how, you will place yourself head and shoulders above individuals who never use an apostrophe because it’s hard to text and type, or even worse, those who use the aberrant apostrophe wherever they so please. Read over these possessive plurals rules to get a better handle on how they function, how they are formed, and how you ought to use them.
Most plurals in the English language end in the letter “s.” A fun trick that many people try is simply adding the letter "s" willy-nilly to any noun, even when the plural form should not end in s, resulting in such silly phrases as “all the womans and mans of the town were gathered.” (Look for more on this in the next section.)
For the vast majority of plural nouns that actually end in the letter "s," the rule is rather simple: add the apostrophe after the s.
Special cases arise, however, when a word or name ends in the letter "s," and you still want to pluralize it. If you’re going to see the house where Billy Robbins, Sandy Robbins, and their children Archibald and DeClan Robbins live, you are perfectly free to use the phrase “the Robbins’s house,” as you are referring to more than one Robbins.
There are plenty of plurals in the English language that are irregular; that is, they do not end in the letter "s." Some of the most common, as alluded to above, are the word “woman” which becomes “women,” and “man” which becomes “men.” You may have forgotten a few other of these uncommon plurals, such as geese, mice, phenomena, and words that lack plurals such as sheep and deer.
For irregular plurals, you must add an apostrophe before the s.
Your dirty bedroom might be the mice’s and geese’s and sheep’s favorite hideout in town; in any case, the “s” comes after the apostrophe. Because you’re so used to Rule 1, Rule 2 may seem counterintuitive at times. You may be tempted to write “the womens’ club,” “the childrens’ room,” “a wolf in sheeps’ clothing.” This is incorrect! Just remember, those irregular plurals do not end in the letter s.
Now that you’ve learned a valuable lesson, you will probably be rushing out the door to place apostrophes on every word ending in “s.” Wait just a moment, however.
One of the most important rules of the apostrophe is that plurals without possessives need no apostrophe. Therefore, the greengrocer advertising “apple’s, pear’s, and peach’s” is totally, utterly wrong. Although the words are now possessives, they are not pluralized.
The proper way, of course, to pluralize these words is by writing “apples, pears, and peaches.” The same applies when you’re talking about Jesus’ teachings and Odysseus’ travels, unless there are several of each walking around, in which case you may use the superfluous Jesus’s and Odysseus’s.
Finally, irregular plurals that still end in "s" such as knives, wives, crises and potatoes should follow Rule 1—simply place the apostrophe after the letter s. The knives’ edges, wives’ stories, crises’ repercussions and potatoes’ colors are therefore grammatically preserved.