In modern standard English, you as second person pronoun serves a multitude of purposes: singular and plural, subject and object, formal and informal. It wasn’t always so.
Centuries ago the language had singular thou and thee, plural ye and you. The numerical distinction then changed to one of register: thou and thee for familiar use and for speaking to children or people of lower social standing; ye and you for marking courtesy or respect.
Gradually ye and you shifted to the default position, supplanting thou and thee, which were marginalised to regional, religious, and archaic use. Then ye began to wane, for a variety of reasons, until you had taken centre stage as the pronoun of choice in singular and plural uses in all registers – but not all dialects.
Hiberno-English is one dialect where ye is found: I grew up using it in the west of Ireland, and I find it extremely useful. Ye behaves much like you: we have yeer ‘your’, yeers ‘yours’, ye’ll ‘you’ll’, ye’d ‘you’d’, ye’ve ‘you’ve’, ye’re ‘you’re’, and yeerselves ‘yourselves’ (all plural).
These are far more often spoken than written, so they’re less codified than the standard paradigm for you. But I would still consider ye’re ‘your’ in this Irish Examiner article an error (yere without the apostrophe is less wayward):
But we didn’t stop at ye. Alongside it there is yous, also spelled youse, you’s, youze and youz, and the more fronted yez, yehs, yiz, yeez, yees, ye’s, yeeze, etc. One reason there are so many is that the vowel is often unstressed (and thus orthographically opaque). But speak to people from around the island and you’ll hear different vowel sounds, even from the same speaker depending on the word’s environment.
It helps to think of these in two main sets: ye and youse. Or perhaps three: ye, youse, and yiz – this is the system preferred by Raymond Hickey (PDF). In my own speech I favour ye, but I use all three types. Ye is a Germanic holdover, but youse appears to be an Irish innovation. T.P. Dolan’s Dictionary of Hiberno-English comments on its emergence:
From the time large numbers of Irish people became exposed to English, in the late 16th century and onwards, the ‘you’ form was therefore the normal form of address to a single person. As regards the verbal forms, there is evidence that in the 17th and 18th centuries some people tried to distinguish between singular and plural by making changes in the verb: we thus find ‘you is’ and ‘you are’; but this useful device was abandoned in the interests of so-called purity of language. Confronted with this bewildering volatility in the use and formation of the second-person pronoun, it would appear that Irish speakers of English decided to distinguish singular from plural by attaching the plural signal s to the singular ‘you’, on the analogy of regular pluralisations . . .
Ye and the y_z forms are not evenly distributed. Jeffrey Kallen’s Irish English (vol. 2) notes a significant discrepancy between the Republic of Ireland and Northern Ireland. Treating yous(e), yez, yowz and yiz as a single group, ye as another, he searched the ICE-Ireland corpus and found 52 youse in NI, 18 in ROI, and 40 ye in ROI and none at all in NI.
While ye is inflected as yeer in the possessive case, youse/yiz may be realised as the remarkable yizzer or yisser. Here it is in use:
‘I’ll book the airport chapel where Lorna and the rest of youse can do yizzer praying for a few minutes, but that’s the end of it.’ (Deirdre Purcell, The Winter Gathering)
‘Why ardent yiz weerdin yisser bleaten c…c…collars.’ [Why aren’t you wearing your bleedin’ collars] (Ross O’Carroll-Kelly, Downturn Abbey)
And a few versions of youse/yiz:
‘Howlt on there, youze,’ said the C.G. (Samuel Beckett, Murphy)
‘I’d say it’d be as well for yeez both if he wasn’t found here.’ (Jennifer Johnston, How Many Miles to Babylon?)
‘Youse took a queer long time, anyway. Would it be too much to ask what yiz were up to?’ (Jennifer Johnston, The Gates)
‘Are yous goin’ to put on th’ gramophone to-night, or are yous not?’ (Seán O’Casey, Juno and the Paycock)
‘From now on yiz can collect yer letters at the post office.’ (Ferdia Mac Anna, The Last of the High Kings)
‘What did yis do to him?’ said John Paul. (Roddy Doyle, The Woman Who Walked Into Doors)
Ye and yeer:
Did ye practise yere piano pieces? her mother asks. (Mary Costello, ‘You Fill Up My Senses’, in The China Factory)
‘That’s all yeers, and here’s mine.’ (Seán Ó Faoláin, ‘The Talking Trees’)
‘Have ye no business of yeer own to mind without nosing round here?’ (Frank O’Connor, The Holy Door)
When she left, Malachy kept saying, Will ye mind yeerselves, will ye? (Frank McCourt, Angela’s Ashes)
And both at once, in Paul Lynch’s Red Sky in Morning:
You’re right. Evicting youse is pure wrong. But if Faller sees ye lumping about – there’s fuck all you can do. […]
Faller and his boys will be over to yous later. Ye know how it is.
Dialects that exclude ye as a normal pronoun still retain it in several niches: fossilised expressions like ye gods and hear ye; biblical sayings like Oh ye of little faith and Judge not, that ye be not judged; old poetry like Gather ye rosebuds while ye may; and old hymns like O Come All Ye Faithful and God Rest Ye Merry, Gentlemen.
The spread of you to dominate the pronominal paradigm in English simplified things, but at the cost of nuance and occasionally clarity. The prevalence and popularity of alternatives – to the Irish list we can add y’all, ye aw, you’uns, yinz, yunz, yupela, and others from the US and elsewhere – suggest that people have found the deficit unsatisfactory.
I asked on Twitter what second-person plural pronouns people used (and their dialect). All the replies can be read here.