Hi Sabiya, and welcome to the forums!
The short answer to your question is that
you and
guys obviously form a unit in which
you determines the reference of
guys. (That is, they form a noun phrase, which functions as subject in your example sentence).
And as with a lot of grammatical analysis, substitution can be a useful tool:
The/these/those guys can come with us. (Then, there is "expansion" - see below ('All...')).
A somewhat longer but still reasonably digestible (in fact, great, very functional!) answer is provided by COBUILD's
English Guides 10: Determiners & Quantifiers (pp 43-44):
3.4 Personal pronouns as demonstratives
So far we have looked at cases where things are being pointed to that are close to speakers or liseners, or far from both. But what if it is the speakers or listeners themselves who are being pointed to? In this case you can use personal pronouns in front of nouns, as demonstratives.
'we' or 'us' for speakers
If speakers want to refer to themselves, they can put we or us before the noun.
We're a selfish lot, we writers.
I heard my parents talking of sending us children away.
'We' is used when the noun is a subject, and 'us' when the noun is an object or comes after a preposition.
We lawyers are paid to take the tough choices.
I hope you don't expect us girls to do the cooking.
The majority of us lads are professional drivers.
You cannot use 'me' or 'I' in this way, or indeed any other personal pronouns.
'you' for listeners
To refer to your listeners, you can use you followed by a noun.
I think you fellows are far too modest.
What's the matter with you people?
This is only possible in the plural. You cannot for example say 'What's the matter with you fellow?'.*
[There is a similar use of 'them' (in non-standard English, as opposed to standard 'those'): 'Did you really see them things like you said?'].
Then there is the "detailed" answer in Huddleston & Pullum's CGEL (page 374): '(T)he determinative counterparts of the 1st and 2nd person plural pronouns
we and
you' are called
personal determinatives** - a term which describes those two items which not only mark the NP as definite but add "person deixis":
we*** as a personal determinative 'denotes a set of similar nouns (plural)**** containing the speaker', whilst
you as a PD denotes 'a set of similar nouns (plural)**** containing at least one addressee but not the speaker'. Furthermore (and relatedly), personal determinatives are 'exactly parallel to other definite determiners such as the demonstratives (this, these; that, those) and the definite article in, for example, permitting the universal quantifier as a predeterminer. Compare:
(All) we supporters of a federal Europe with
(All) those supporters of a federal Europe and
(All) you students with
(All) the students. This property distinguishes them from the personal pronouns, which permit
all only when postmodified:
All we/you who support a federal Europe will win the argument, but not *
All we/you will win the argument. In the following examples however,
we and
you are pronouns:
We, the supporters of a federal Europe, will eventually win the argument and
You, the students, should form a society. (Here, the determiner of
supporters and
students is clearly the definite article, and the NPs formed with it are full NPs in their own right which stand in supplementary apposition to the personal pronouns
we and
you. Note that all the personal pronouns can occur in the appositional construction, but that only the 1st and 2nd person plural pronouns can be personal determinatives).'
There is a fair bit on 'apposition' (too much to type up), which is perhaps the first notion/term that most people would think of in relation to your question (it's what I did, anyway!), in the CGEL and elsewhere, but the above stuff on 'personal determinatives' would seem to be more what you're looking for.
(
http://www.phon.ucl.ac.uk/home/*beep*/enc/index.htm
>
http://www.phon.ucl.ac.uk/home/*beep*/enc ... apposition )
Finally, regarding examples like 'You all are here today', the COBUILD English Guide mentioned above seems to view and label this as simply a case of "delayed"-
all (i.e. it then comes after the noun it is referring to), whilst the
COBUILD English Usage has this to say:
All: used after the subject
'All' can also be used after the subject of a clause. For example, instead of saying 'All our friends came', you can say 'Our friends all came'. When there is no auxiliary, 'all' goes in front of the verb, unless the verb is 'be'.
Their names all began with S.
We all felt a bit guilty.
If the verb is 'be', 'all' goes after 'be'.
They were all asleep.
This is all new to me.
If there is an auxiliary, you put 'all' after it.
It will all be over soon.
We don't all have your advantages.
If there is more than one auxiliary, you put 'all' after the first one.
The bedroom dresser drawers had all been pulled open.
'All' can also come after the direct or indirect object of a verb when this object is a personal pronoun.
We treat them all as if they were china.
I really do hate you all.
*Or rather, one perhaps
could say 'What's the matter with you[,] fellow?', but then it would be more a quite strange-sounding
vocative (and obviously in the singular).
**H&P use 'determinative(s)' as a part of speech/category/class label, and 'determiner' as the syntactic FUNCTION (i.e. "higher-level") label. I think. (
). See chapter 2, esp. sections 4 and 5~ of their
A Student's Introduction to English Grammar (previewable on Google Book Search), or:
http://forums.eslcafe.com/job/viewtopic ... 938#759938 . (
).
***
Us i.e. accusative/objective case seems more suited to object role than nominative/subjective
we. Examples from page 462 of the CGEL:
Nobody asked us workers how we felt about it; %
The real work of universities...is now being made increasingly difficult for we workers; %
What a delightful innovation, for we workers to submit something to your splendid publication. (% in the CGEL denotes 'grammatical in some dialects only' (but not really in "Standard English")).
****My addition of 'of similar nouns (plural)' to 'a set'.