When “one of” many things is itself plural

"is" is fine here. "is" goes with "one" - you are referring to one of the things you believed in.

You would use "are" if you were to say:
There are all sorts of things I believed in then which I don't believe in now. Language rules set in stone and unchanging pronunciation are two of those things.

The subject of the verb, "language rules," is plural, so it needs the plural "are."

I'd say "... and language rules set in stone are among them."

The rule might seem complicated but it's really not. When referring to many/more than one use "are" when referring to one use "is". When you're referring to an object with many items but only the one object, it's still singular. A list may have multiple items but as an object it's still only one thing. If you're talking about many lists then we're back to multiples again.

Thanks Ing and JAC for confirming my thoughts. I had written it (with 'is') without thinking and then thought it looked a little odd. I realised later that one way round is to reverse it:

There are all sorts of things I believed in then which I don’t believe in now, and one of them is language rules set in stone.

@Tom - I think the point is that 'language rules set in stone' is a single notion, one of several areas where I've changed my opinion. eg (for argument's sake):
Santa Claus, religion, political ideas, language rules set in stone

Lol, yeah, I don't really like spouting the stuff that was drilled into me when I was young but having an English teacher for a grandmother was more than any poor kid should have had to put up with.
Thing is, I doubt I'd've been anywhere near the reading junky I am now without it. I also owe her for my vocabulary, total lack of fear of speaking in public and at least SOME of my grasp of logic and the the other two languages I speak besides!

Personally, I believe "language rules set in stone" is plural, simply because of the word 'rules'.
The true problem lies in the syntax.
I concur with Tom - the sentence flows better by changing it to "...language rules set in stone are among them."
Another idea might be to change the quantifier 'set in stone' to an adjective like 'immutable' or 'uncompromising' -- this makes it much clearer that the subject is plural and should be accompanied by 'are'.

@Becky ... Yu'r joking right? Immutable? That's just a bit "pretentious" don't yu think? That word as snob written all over it. Just who the heck would put "immutable" or the mouthful-of-syllables (and dull) "uncompromising" in stead of "set in stone"?

There's nothing wrong with the syntax. It flows fine with the verb "is". The driving word is "one" not "rules". If yu read the sentence out loud as written with "are", it should grate on yu; it should make yu shudder. I had trouble forcing myself to say "are".

"Is" is right.

In addition to what AnWulf said, I would like to comment that, yes, it is possible to change words/phrases/clauses to make a particular word choice correct, but that is not what the question was about.

For example, if I present a sentence: " There are eight inches between the two ends of this stick. ", and if my question is (for example) "Is eight inches" correct or is "eight-inches" correct? -- Helpful responses would focus on that, and not just say something like: " Change the sentence to: This is an eight-inch long stick. "
(unless, of course, the entire original sentence does not make sense).

Like Warsaw Will I often have to think a bit about sentences like the example he quotes.
If one uses a different verb does it make the decision any easier?
"Language rules set in stone make(s) me shudder"
Collective nouns in English seem to cause a lot of people (especially Sky Sports commentators) problems.
Consider:-
"The crowd is/are large"
"The team is/are playing badly"
"Manchester United is/are a great team"

Does "language rules" qualify as a collective noun or is language merely an adjective governing the plural noun "rules"?
If the former then 'is' would be correct, the latter would require "are".

Another example:-
The rules of the language is/are clear?
I think the answer to that one is clear.

Is a verb not controlled by its subject?
She makes pancakes. They make pancakes.
She is alone. They are not alone.
Language rules are something that must be obeyed.
Why should the use of one as part of the object change the verb?

@AnWulf - No, I'm not joking. Words only have a feeling such as the one you mentioned if you assign it to them. They are just words. I chose that word for its definition; it seemed quite fitting as a replacement for 'set in stone' as it is defined as: Unchanging over time or unable to be changed -- which is what I believe the OP was getting at when they were using the original adjectival phrase.

You may be correct that it isn't about syntax, but what I am saying is that I agree with Tom in that it would be much easier to avoid the problem altogether by using different words to get the same point across.

When you're choosing your verbs you have to pay attention to the plurality of the subject. The second half of the sentence without the conjunctive 'and' can stand as an independent clause; the subject of it is 'language rules' which is plural. According to subject-verb agreement rules, if the subject is plural, the verb form must match. The most simple solution to this problem is to follow Tom's advice and say:

"language rules set in stone are among them." using ARE and not IS because 'language rules' is plural. Whether or not it sounds better given the words involved is not the point. The correct answer is ARE because of the plurality of its subject. Tom is and has been correct the whole time.

Also @AnWulf - does your 'o' button not work?

Becky,

There is a difference.
Consider these sentences (ignore the factuality of these examples!) :

1. Children playing basketball at night is bad.
vs
2. Children playing basketball at night are bad.

Both are correct (but, of course, have different meanings). The sentence in the original post by WW is like number 1.

Oh wow, fun times!
First, I'll address Becky (btw, AnWulf's o button does work as you can see the o in other words... and it also bugs me that Anwulf types "yu"):
Anyways, to my point. Re-read J Anthony Carter's first post. It describes the answer most simply. When considering the original sentence, 'language rules set in stone' is one object on a list of many objects. Regardless of whether that object has more sub-objects, the correct word can only be 'is'. It doesn't matter if you change 'set in stone' to whatever else you want; 'language rules' is a singular noun in this context (and context is everything). Changing it's adjective does nothing to the requirements of the verb.
After re-reading your last post, it seems that the idea you're having trouble grasping is that 'language rules' can be a non-plural noun. I assure you, in this case it is.

Moving on to Hairy Scot's post: As a standalone sentence, "Language rules set in stone make me shudder" does not use 'makes' because the subject is given to be a plural group. There is no context given to show it as a singular object of a larger group (and remember, context is everything). As for your other examples, the sentences you give each have a singular noun as their subject. Both crowd and team are non-plural. The individuals within those groups are plural, but the group is singular.

@Hacovo - Thanks for the comment. Just on the crowd, team thing, there is a difference between American and British usage here, as has been mentioned on other posts. Americans tend to prefer formal agreement, in other words use a singular verb, whereas Brits usually go for notional agreement, using a plural verb with group nouns such as crowd, government etc.

"In British usage government, in the sense of a governing group of officials, takes a plural verb: The government are determined to follow this course" - Free Dictionary

English: the only world language that causes confusion between two different people speaking the same words ;)

@Hacovo
To paraphrase George Bernard Shaw:
United Kingdom and United States, two countries divided by a common language.

:)

@Hacovo
I am aware of the correct form of the verb to use with collective nouns.
The examples I gave are some that people, especially UK sports commentators, often get wrong.

I can see how people are trying to figure out the answer by looking at "rules" and "one" in the sentence, but totally missing the fact the important word is "stone". Suddenly the whole problem goes away - "Rules set in stone" refers to a single object - the "stone" in which the "rules are set." There were ten commandments, but only two tablets. In this case there are many rules, but only one stone.
"Is" is the correct answer.

I know this is a 'dead thread', but I believe the problem lies with the subject and object. The current subject: "language rules set in stone" has an adjective and participial phrase, making rules the subject and requiring are as the verb. The object: "one of them" conflicts with the subject-verb agreement. It would be easier to flip the object and subject: "and one of them is language rules set in stone".

I'm with you on this, Warsaw Will. If you replace the pronoun with the noun phrase it is obviously "is": "There are all sorts of things I believed in then which I don’t believe in now, and language rules set in stone is one of the sorts of things I believed in."