This might be of interest: an article linking to research on the conversational benefits of 'so': http://www.theguardian.com/education/2015/apr/07/research-into-using-so-move-conversation-along

I'll ignore all the historical / social stuff, which I suspect is a lot of 'golden age' bunkum; rear-view mirrorism, I think it's called; you know the sort of thing: 'back in the good old days', 'nowadays everything's being dumbed down', and so on. Whereas I imagine that if you used any objective criteria like overall exam results etc, this fear would be found to be groundless.

However, I do think JohnH makes one good point. There is an unfortunate propensity on this forum to ascribe motives such as pretentiousness, or even worse 'middle management' pretentiousness, to people who use language the commenter doesn't approve of, and I think that smacks of a certain intellectual snobbery. Which I think is rather sad.

I am fascinated though as to what JohnH means by 'linguistic excellence'. One dictionary defines linguistic as 'connected with language or the scientific study of language', and surely the main function of language isto communicate with other people. Now I think a lot of London street traders communicate excellently with their customers, although not in a language that is considered Standard English; most mothers communicate excellently with thier babies, but perhaps not in a very elegant way - is this what JohnH means by linguistic excellence? I suspect not.

I tried googling "linguistic excellence", and apart from a lot of references to the "linguistic excellence of the Koran" and other religious texts, all I could find was stuff about people who are able to learn a lot of languages, and the role of language in Ancient Greece and Rome. But I did find a couple of references in academic books:

"Consequently, from the point of view of general linguistic excellence, nothing matters except the ability of the sentences in that language to convey transparently and without ambiguity their meaning", Stephen Everson, Language, Cambridge

By this definition, my London street trader and mum would qualify as having linguistic excellence, I imagine. But many people would no doubt come up with a definition more like this one:

"The view of language was a monodialectical one in which the role of language education was to eliminate (through the use of sanctions) variant forms, thus maintaining the language's imagined purity, and to impose norms of perceived linguistic excellence, thus safeguarding its future. Linguistic change of any kind was widely perceived to be deterioration", ed. Rebecca S Wheeler, The Workings of Language, Greenwood (talking about 18th and 19th century prescriptivism).

Which brings us back to the old question of who decides what is 'correct', and what is 'excellence' (and in what contexts). If 'linguistic excellence' here is closer to the first definition, then perhaps it's worth striving for. If it's more like the second, it's just the old prescriptivism in a different guise.

Although 'Is it you who are' is the gramatically 'correct' answer, I'm increasingly convinced I'd normally say 'Is it you who's ...' or use a workaround.

A similar problem with a relative clause came up in class the other day in an exercise on tenses from a book called Grammarway Advanced. There was a question where the students had to fill the gap with a suitable verb in the appropriate tense, includinng the word 'ever':

"This is one of the best books that ................ on the subject"

The students were obviously meant to pick the present perfect passive of 'write'. And my first reaction was:

"This is one of the best books that has ever been written on the subject". But then I started thinking: the relative clause refers to 'books', not one, just as the relative clause above refers to 'you', not 'it'. So maybe it should be 'have', not 'has'. It turns out this one has been bothering people for centuries. Although Fowler thought 'has' here a blunder, it's been used by many good writers. It seems that 'one' is just too strong a draw for most of us; it's that oldidea of notional agreement taking over from formal agreement.

I think it's the same with 'Is it you who are'. Formal agreement favours 'are', notional agreement favours 'is'. And in spoken English, at least, notional is often more natural and idiomatic than formal or 'correct'.

@AnWulf - No, the teacher is Polish. I think the 'mates' bit was the words my student used.

@HairyScot - One of my English teachers used to give this example of the oddities of English:

' "Now, then", he said, giving me a pretty ugly look.'

'Pretty' was prety popular with British writers in the eighteenth and nineteenth centuries, especially with Daniel Defoe. Johnson gives eight examples, presumably approvingly. Even Lowth, and other grammarians used it in their books.

As to meaning, I like Johnson's definition best - 'it is less than very'. I can see why you might want to avoid it in academic texts (although both Darwin and Ruskin used it), but I would have thought that the same goes for 'very', so I don't really understand those who say use 'very' instead. For me, at least, they are not the same: 'petty' is more nuanced.

Judging by its use in books, the plural is the norm; this is from Thackeray, ' "It is you who are cruel," cried Pen'.

I think in informal English, however, we might well say 'It's you who's wrong'; 'are' sounds a bit stilted somehow.

My explanation would be is that this is a cleft sentence where 'It' is an introductory device, the subject of 'is', and 'who is wrong' is a specific type of restrictive relative clause modifying 'you'. The verb should therefore agree with the subject of the realtive clause, 'you', not 'it'.

Compare with a couple of more obvious plurals:
"It's the Johnsons who have just been to Cypress, not the Smiths." (Not 'has')
"It's oysters that make me feel ill, not mussels." (Not 'makes')

@Dean. I think you're cheating a bit with almond and dinghy, and perhaps even with honour. There are still sounds there; they wouldn't sound the same if you take away the letter altogether, as with 'listen, hour' etc. The 'gh' in dinghy is a specific sound, /ŋ/, not just g and h together, otherwise it would be 'dinhy'.

/ˈɑːmənd/
/ˈdɪŋi/

and even with honour, /ˈɑːnər, the sound of British 'ou', or American 'o' is not 'u', but the schwa.

As I've said before, I know nothing about football, and so nothing about 'iPro Stadium' without going to Wikipedia myself, so I think perhaps you should start doing a little research of your own. As for foreign stadiums, just Google them and see what results you get. But if in doubt add 'the'.

These are both 'reduced relative clauses', and both are passive (present simple passive and present continuous passive):

1. The instruments (which are) used are very reliable.
2. The instruments (which are) being used are very reliable.

The meanings are very similar, the difference being the normal one between using present simple (1) and present continous (2) forms

The first one suggests you are talking about a standard process, situated in general time, which is fairly static. The second sugegsts that you are talking about a situation occurring now. For example:

'We have been operating this procedure for some time now, and the instruments used are very reliable'

'This is a new procedure, which has its risks, but a least we know that the instruments being used are very reliable.'

Wake up, HS, it's morning again :). And the subjunctive, and especially the use of 'were/was', being one of the most controversial areas of grammar, I doubt it will ever go away.

My discussion with jayles has been purely historical, and I've learnt a little about Old English along the way.

But when someone like EnglishElle calls herself a 'firm believer in descriptivism', and goes on to contradict that in everything she says, I will react, especially when she puts it down to lack of education. She might try reading a modern grammar book for a start before throwing about that sort of accusation.

But, HS, one or two people saying something doesn't make it common usage. Common usage is what is generally used and/or accepted by educated speakers and writers of a given language community, not 'anything goes'. This expression is used in the plural mainly in the States, and if you check the New York Times, for example, the entries are nearly all for "attorneys general" - that *is* the common usage.

Here there is a certain logic to it, but there are other language contexts where it is only common usage that makes something 'correct' , especially in vocabulary. It is because of common usage, not any written grammar rule, that most of us don't say 'thou art' any more, or that English moved away from inflected endings to the use of auxiliaries, and all the other changes that happened in English before any grammarian put pen to paper.

And what did the first grammarians use a basis for their rules - the observation of common usage.

And on the subject of compound nouns, is there any rule for deciding whether they spelt as two words, hyphenated, or joined together? None that I know of, except common usage.

As for Nick D's idea - passer-by, and brother-in-law are also nouns in their own right - but passer-bys and brother-in-laws certainly don't sound OK to me. Why? Because it's neither common usage, nor is it logical, as mshades explains (he explains a lot more than the history). Same difference with attorneys general - they are general attorneys, not some kind of general.

And what about expressions such as spoonful, cupful, bucketful and truckful. Logically you might think it should be spoonsful etc, as this commenter on a forum suggested, "The grammatically correct answer is "spoonsful", those who say otherwise are mistaken. However, those who say otherwise also have custom and usage on their side, and "spoonfuls" is perfectly acceptable. "

Some people think 'spoonfuls' is recent, but I'm not so sure. According to Ngram, that has always been the case, although 'spoonsful' got close in the first half of the 19th century. And according to another grammar book, this time from 1830, "The words spoonful, mouthful, and others of a like kind, are indivisible compound nouns, therefore must form their plural regularly", a point echoed in several books of that time. And why are they 'indivisible'? I would suggest through common usage.

So, what many people seem to think is the 'grammatically correct' version has in fact been dismissed in many grammar books. Which simply confirms me in my belief that there is only one unbiased, objective way of deciding whether to use one form or another, and that's common usage. And to be very wary when someone says 'the grammatically correct answer is ***'!