@jayles - I'm not sure that the rest really are a problem, as students might well not use 'if' in their L1 in these circumstances, and I've never had a problem where a student is trying to analyse one of these, and gets bothered because they can't fit it into one of the five categoeries (0,1,2,3,Mixed)

By far the biggest problem, at every level I'd say, is will and would after if.

@jayles - Thank you for confirming my suspicions, but why then doesn't that apply to time clauses in 3rd conditional, where we are using a 'real past', not an 'unreal' one?

Conditionals cause problems for students at all levels, so I wouldn't accept your 'intermediate crutch' description. I know it's fashionable to knock 1,2,3, but it has its uses, is flexible (increase in tense possibilities at higher levels) and probably covers the vast majority of conditional sentences that students are likely to need. I did a little experiment with The Little Prince, and 70% of the conditional sentences there fell into the 1,2,3 pattern, and nearly all conditionals where the result depends on the condition fit into this pattern.

Here are some that don't fit:

'If you're hungry, there's some ham in the fridge'
'If Mike didn't do it, who earth did?'
'If Sam doesn't like jazz, he should have said so.'
'If she hasn't called, she could have lost our number.'
'If I'm to get this essay done, I'll have to forget about going to the pub tonight.'

But none of these involve a real condition and result. At least three mean 'if it's the case that'

In fact, if native speakers had also learnt this system, there might not have been so much nonsense written on the Internet about Snow Patrol's Chasing Cars. Many of those (correctly) commenting on forums that Snow Patrol were absolutely correct have in fact been foreign learners, who seem to understand the theory of conditionals rather better than many native speakers.

Just spotted in a piece by David Baddiel at the Guardian:

"Three years ago, me and my brother Ivor made a short film for Kick Racism Out of Football called The Y-Word ..."

http://www.theguardian.com/commentisfree/2013/sep/17/david-cameron-yid-really-is-race-hate-word

@grammarhack - perhaps I'm too old to have recognised that as hip-hop talk, and as hip-hop came out of black culture, not surprisingly it owes a lot to that culture, just as jive-talk came out of black jazz culture in the 50s. In any case I wasn't accusing you of being racist, although I might have been hinting at a certain stereotyping. I apologise if I jumped to any conclusions, but AAVE has come in for a lot of (ignorant) stick on these pages.

Whatever you call it - 'But instead I be writing informally as it be more friendly. Me and yo now sees eye to eyes' is not informal Standard English. Just as 'I done it yesterday, didn't I?' (London) or 'We was in t'pub where t'beer were nowt to write home about' (Yorkshire) or 'it's well wicked, innit?' (British youth culture) are, (although the last one is perhaps borderline).

The important thing to recognise about the use of dialect is that it has nothing to do with laziness. Dialects have their own rules; they're just different from those of Standard English, that's all. More about what is and what isn't Standard English in the first document listed here:

http://www.phon.ucl.ac.uk/home/dick/standard.htm

The term informal English is simply used by linguists and ESF/EFL teachers to mean normal spoken English, as opposed to the more formal varieties of written English. Perhaps I should have clarified that 'Me and Dave are going to the pub' is very informal, but it is undoubtedly still Standard English.

But back to can and may, there's a one word answer - context, just as we do with words that have more than one meaning all the time. Just as we use context to differentiate between the two main meanings of may:

It may rain this afternoon.
You may get down from the table now.
I am just going outside and may be some time. (attr Laurence Oates)
May I just say what a fascinating discussion this has been.

'As you have made them acceptable to be used as synonyms' - well as I've already pointed out, that's not exactly what I said, but if it's true, you flatter my powers of influence:

http://books.google.com/ngrams/graph?content=Can+I+go%3Aeng_us_2012%2CMay+I+go%3Aeng_us_2012%2CCan+I+go%3Aeng_gb_2012%2CMay+I+go%3Aeng_gb_2012&year_start=1900&year_end=2000&corpus=15&smoothing=3&share=

Interesting that the change is even more marked in your variety of English than mine.

Your kids can rest easy, by the way, I teach foreign adult learners, for whom it is very important to recognise the differences between formal and informal, what is appropriate where, when and with whom (See, even I can get formal when I want to). And I don't know why you continue to insist on making this a personal attack; I'm very much in the mainstream. Interesting that you use the word 'assert' in your last sentence, as much of what you have been saying is just that, pure assertion.

http://www.volokh.com/2011/10/04/descriptivism-prescriptivism-and-assertionism/

Hi Jasper, this is a weird one, and no, I do mean after, although the action started before. Writing about time clauses on my blog I wrote 'Occasionally we use Past Perfect with before to talk about the completion of an event which started earlier but finished later than the other event.

"She stormed out of the room before I had even finished what I was saying."

The order of events are:

1. I started to say something
2. She stormed out of the room
3. I didn't manage to finish what I was saying

In MyGrammarLab Advanced (Mark Foley and Diane Hall), they say - 'With before + past perfect, the action in the past simple happens first: "I left university before I'd finished the course I was taking",' and go on to say 'we can use this pattern for a past action which prevented a later action from happening: "She sacked him before he'd had the chance to explain" '.

Their first example, where they've used past continuous rather than past perfect is quite interesting in relation to your question. Apropos, that was a really good question, and has inspired me to try and write a blog post on time clauses within if-clauses in conditionals.

My conclusions so far are that we use real past rather than unreal past in time clauses in past hypotheticals (third conditional), and present probable conditionals (first conditional), and was leaning towards the idea that that could be the principle, but it rather looks as though we use unreal past in present hypotheticals (second conditional), which rather puts the kybosh on that.

As far as I can see, these sound more natural keeping with the unreal past, than with present tenses. What do you think?

If you saw a deer while you were (are) out walking, what would you do?
If she turned up out of the blue when you least expected(expect) it, what would you do?
If we arrived at the party after everyone had left (has left), it would be very embarrassing
If we arrived at the party before it had (has) really got going, it would be equally embarrassing

@grammarjack - I don't know what world you live in, but the majority of business correspondence these days is relatively informal (e.g. use of contractions, first names), largely due to the rise in the use of email. When I started work people still started business letters with 'Thank you for your letter of the 27th ult.', which I doubt many people nowadays would even understand.

Why on earth would I want to use anything but normal language on a forum like this?

It's sad to see you've slipped into the same insulting mode as Over50guy. And it's perhaps telling that you chose African American Vernacular English to make your (humorous?) point. Which is totally irrelevant, incidentally, as that is a separate dialect, not an informal version of Standard English, as any linguist will tell you.

But shouldn't you be directing your remarks at the people who wrote them, the editors of The American Heritage Dictionary, seeing you obviously have a much better grasp of the principles of English grammar than they or the editors of the Merriam-Webster Dictionary do. Apparently better than the whole world of ESL/EFL and linguistics, for that matter.

@grammarhack - First of all, thanks for taking the time to read my post. The reason I say ‘maths’ and not ‘math’, incidentally, is because that’s how it’s referred to just about everywhere in the English-speaking world except for North America. But as it happens, on language forums and on my own blog I do tend to write fairly informally, as I find that friendlier.

As regards referencing my own post, of course I wasn’t putting it forward as any sort of authority, but as I had already written on the subject of 2+2=5, it seemed a shame to let it go to waste. As for truth, I’m not sure where that really comes into a discussion about language.

I'll come back on your main point about formality vs correct a bit later. But for now just a word about 'can' for permission. I don't think I exactly said that 'can' and 'may' are synonyms, but I did say 'Nowadays, when used in conversation, may (for permission) can often sound over-formal and a bit old-fashioned', and quoted Michael Swan, author of Practical English Usage as saying ‘In an informal style can and cannot / can’t are more common [than may and may not]’.

This isn't exactly revolutionary stuff. Here’s what they have to say at about.com, which has one of the biggest (American) ESL sites:

“In the past, especially when discussing modal verbs' grammar, 'may' was considered correct and 'can' incorrect when asking for permission by many teachers. However, in modern English it is common to use both forms and considered correct by all but the strictest of grammarians.”

http://esl.about.com/od/modals-for-intermediate/a/Modal-Verbs-Grammar.htm

At Merriam-Webster's Dictionary:

“The use of can to ask or grant permission has been common since the 19th century and is well established, although some commentators feel may is more appropriate in formal contexts.”

And at The American Heritage Dictionary:

“Generations of grammarians and teachers have insisted that can should be used only to express the capacity to do something, and that may must be used to express permission. But children do not use can to ask permission out of a desire to be stubbornly perverse. They have learned it as an idiomatic expression from adults: After you clean your room, you can go outside and play. As part of the spoken language, this use of can is perfectly acceptable.”

And for a linguist’s view of the historical aspect and a graph that says it all really, there’s Motivated Grammar:

http://motivatedgrammar.wordpress.com/2012/12/05/can-i-may-i-the-historical-perspective/

@jayles - but what I don't understand is why the name on the RSS reader should be different from that on PITE's page. It's not just you; Brus always appears on my reader as Retired Teacher.

@jayles - I'm confused. When you were just plain jayles, you registered on rss readers as jayles the unwise. And now that you've 'come out' as jayles the unwise, my rss reader is callin you 'jayles the greedy'! Which is it to be?

@Over50guy - It's always easier to throw out personal insults than put forward a constructive argument, but we're used to something a bit better on this forum. There are a few regulars here who I often disagree with, but none of them have yet accused me of being ignorant or uneducated.

I may be informal on occasions, but at least I'm polite. And in my experience people are generally judged more on their manners than by the way they talk.

As for being ignorant and/or uneducated, perhaps you might like to look at my post on personal pronouns at my language blog and judge for yourself, in particular the section titled 'Personal pronouns at the start of a sentence'.

http://random-idea-english.blogspot.com/2011/10/personal-pronouns-subject-or-object.html

Like it or not, the 'Me and so-and-so' construction is quite common amongst educated speakers in informal contexts. Or, as Burchfield puts it in The New Fowler's, contexts 'in which me is now tending to usurp the territory that logically belonged to the subject-pronoun I', including when it is 'used informally at the head of clauses' and he gives several examples, including one from Margaret Atwood and another from Alec Wilkinson, both highly-considered writers. Merriam-Webster Dictionary of English Usage also has one from Flannery O'Connor from a letter written in 1950 - 'Me and Enoch are living in the woods'. So it seems I'm in good company!

Here are two other examples I've come across:

'Me and Barry used to work together.' - from the BBC TV comedy 'Not going out', from a character who spoke absolutely standard English.

'Stan Carey, me, and Dominik Lukes all wrote posts ... about non-literal uses of literally' - American linguist, Gabe Doyle, writing at his blog MotivatedGrammar

@grammarhack - Ah! The language rules are like maths rules fallacy:

http://random-idea-english.blogspot.com/2010/11/in-language-two-and-two-can-be-four-or.html