In the example sentence, "Their understanding of the subject is as good as their masters," the actual thing being compared is the understanding of their masters. The sentence therefore requires a possessive form for "masters", e.g., "Their understanding of the subject is as good as their masters'."
Which possessive to use (singular or plural) depends on ...
Attempting to analyse sentences in isolation runs counter to what language as a system of communication is. There is no way to disambiguate the plant has buried leaves without further context and/or discerning the speaker's intentions. I.e., no you can't tell whether the finite verb is has buried or has in this sentence.
There's nothing wrong with the possessive marker at the end. Compare The king of England's crown, where the -s is at the end of the noun group.
It does sound a bit more awkward if you have a whole apposition following the head noun, but syntactically it looks fine to me.
Or you could write It is my gym instructor Anne's birthday.
Your question is actually a perfect storm in which rules of puntuation dictated by grammar clash with the deeper grammar of spoken English, though rarely with the noun in your example.
Unless you are in the unfortunate situation of having only one single solitary friend in the world, in your example the proper name Adam is a restrictive appositive, that is, ...
"Disease symptoms" is a correct, or at least by far the most common usage.
Google search "Lyme disease symptoms" gives 537,000 results and "Lyme disease's symptoms" 242 results.
In "disease symptoms," disease is not a possessive noun but a noun adjunct or modifier. Similar examples are chicken soup and brick wall.
And if anyone disagrees with this...in ...
Alzheimer's is correct. There is no double possessive in the English language. You can chain possessives (as in your example St Paul's Cathedral's arches). You can also shorten noun phrases (Alzheimer's disease routinely gets shortened to Alzheimer's).
From what I understand, you are talking about multiple friends with children, so the first one is correct, just an apostrophe after the plural. The second one would be correct if you were talking about one friend with children.
Your second guess is correct:
Agent 2's ball
The ball is owned by 'agent 2', which is a noun phrase. You should put the apostrophe indicating possession after the complete noun phrase, regardless of whether the noun phrase includes numbers or not.
You can see this form when referring to royalty:
King Henry V's advisors
or to government and military ...
Since the spelling of the plural of "Master's degree" appears to vary depending on what style guide you follow, I thought I would post an answer that goes into more detail on the possible linguistic bases of using a singular or a plural form.
The behavior of irregular genitives such as men's/man's or child's/children's appears to provide some support for ...
The spelling of the plural of "Master's degree" appears to vary depending on what style guide you follow.
What style guides have to say
Johns Hopkins Bloomburg School of Public Health's style guide
Multiple master of arts (or master of science) degrees
Under no circumstances is the form "masters" (an "s" with no apostrophe) appropriate.
Use the ...
I couldn't find much, but did find an explanation in a scholarly edition (published originally at the end of the 19th century) of William Caxton's Blanchardine and Eglatine from ca. 1498. There must be more modern info sources available, but I didn't happen upon them..
According to the editor, in the 14th and 15 centuries there was a movement away from the ...
Whilst I agree with the answer given by @R Mac, that the plural possessive apostrophe is required, I don't think I would write it like that, and certainly I wouldn't say it.
The problem is that the apostrophe is needed simply to provide grammatical clarity. And when speaking a listener cannot perceive the apostrophe.
I would say:
Their understanding of ...
I would recommend this: "Residents' Parking" because the intent is to provide clarity. Who is allowed to park there? My interpretation of those words means that this area is where (only) residents may park, and there is more than one resident, so it should be plural possessive.
If it were a single parking space meant for one residential unit, then "Resident'...
There’s pendant, and pendulum, both of which literally mean a loose-hanging thing. The trouble is that they have become much narrower in meaning over time because of their associations with specific things. Pendant has come to mean a dangling piece of jewelry. Pendulum has come to mean a precision device, because of its association with clocks and other ...
Use "Mary Queen of Scots' [or Scots's] birthplace."
When a title is integral to the name, it still takes a possessive case. Hence:
Alexander the Great's horse
Catherine of Aragon's husband
The King of the Britons' [or Britons's] retinue
There's at least one example of a writer's guide from the early 20th century prescribing this usage for ...
As in, "The Woodses' friend," a phrase which is excruciating to say aloud.
There does seem to be a fair amount of confusion on the subject, but it seems like the "rules" are fairly straightforward. The general idea is that names follow the same patterns (of pluralization and possession) as any other noun, with the exception that names ending in y ...
At least in the case of "1960's soul to 1990's house," I share Colin Fine's view that you don't need an apostrophe at all. Some style guides undoubtedly differ on this matter of punctuation—as they do on many others—but a number of major style guides the oppose using an apostrophe before the s in decades or centuries rendered as numerals.
From The ...
The difference between the two sentences is that in the first, "population" behaves as an adjective that modifies "quality of life" (and "the" refers to "quality of life"), and in the second "the population's" is a possessive (and "the" refers to "population"). You can find the first usage with other words, like in "Increase the population density" (as ...
If you are using the noun phrase young me to describe yourself in the past, then adding an apostrophe and s to form the possessive would be normal.
Young me was quite precocious.
Young me's toys were all red.
Having said that, it's unusual to use young me in the first place. More typically, a variation would be used:
When I was a child, all of my ...
Swan in Practical English Usage has an entry called noun + noun: advanced points. In the parts section (p360) he states:
We use the 's structure to talk about parts of people's and animals'
a man's leg -- an elephant's trunk -- a sheep's heart.
But to talk about parts of non-living things, we usually use the noun + noun
This seems to be a pertinent question as I haven't seen this discussed in any grammar or on this site.
When the noun phrase ends with a noun we are quite happy to put an 's on the end. This is often described in grammars as the "King of Spain's daughter" or some similar phrase and is discussed on SE here. However, since the 's can only be added to a noun, ...
Without more substantial rephrasing, it will sound strange even if it is technically correct.
It would be more natural if you simply drop the use of the possessive:
Here is the completed assignment of my partner, Jane Doe, and me.
If UEFA is pronounced (or possibly even only thought of) as an initialism, standing for Union of European Football Associations, then the definite article is required. In this case, the article relates to the noun immediately following, that is, UEFA not committee:
A member of the Union of European Football Associations' executive committee...
A member ...
If you turn the sentence around it’s easier to see the answer.
The planets’ sizes are written here (many so it’s ‘they are’)
The planet’s size is written here (meaning, one planet so it’s ‘it is’)
The doors of 100 houses are 100kg (you mean, ‘weigh 100kg?’ (many doors = they are)
Mens’ noses are bigger than those of women (men’s noses - they are - ...
If you wish to make a possessive of a longer title — grammatically a noun phrase consisting of a noun and an appositive — you may attach an ’s to the end of the phrase. Since Scots is plural, however, you only add an apostrophe:
Their demands were equally uncompromising, including the restoration of traditional Catholic worship, the trial of Cecil, the ...
Those titles have different meanings.
"My Articles'/Reviews' Comments" should show all comments, made by any user, on your articles and your reviews.
"My Article/Review Comments" should show all comments, made by you, on an article or review made by any user.
The key point here is that in "My Article/Review Comments," Article or Review are adjectives (...