Don't touch the actors and they won't touch you

The 'normal' way of making a conditional in English is with an 'if'-clause:

If you hurry up, we'll be in time for the train.
We'll be in time for the train if you hurry up. 

There are plenty of others too, of course (As long as you keep walking, we'll be in time for the train) and of course -- isn't it always -- it's much more complicated than this, but there's also a cool way of doing conditionals with and and or.

Consider this warning, which I saw at Dreamland in Margate at their Screamland Hallowe'en thing a couple of years ago:

Don't touch the actors and they won't touch you.

Poster for 'Screamland' in Margate

You could interpret that as an instruction combined with a simple statement of fact: the instruction is not to touch the actors, and the statement is a reassurance that they won't touch you, independent of the instruction. That might in fact be what is intended here, because even if you do touch the actors, they're probably still not supposed to touch the visitors.

But we're funny things, humans, always looking for connections, patterns, reasons, and causes. Those two things being joined makes us want to think that there is some meaningful link between them. It's like if someone says The car is making a funny noise and Jen borrowed it yesterday. You can be pretty sure they're blaming Jen for the funny noise the car is making, and not just telling you two unrelated facts about the car.

Generally, in an and sentence, both bits are the same type: both statements, for instance, in which case they must both be true (so for the sentence about the car to be true, it must be true that it's making a funny noise and that Jen borrowed it -- notice that the inferred link that Jen was to blame does not have to be true). Or they might both be instructions, in which case you're expected to obey both (at the same time or in order), as in Sit down and shut up. Our example sentence, about the actors, is a mix of an instruction and a statement. So we might be expected to obey the instruction and for the statement to be true. I don't know about you but I don't really know where I stand right now, as there is no obvious link between my obedience and objective truth.

It would make so much more sense if, say, the truth of the statement was conditional on me obeying the instruction. So if I don't touch the actors (obey the instruction), then it will be true that they don't touch me. And all of a sudden, we have a conditional like the 'if'-clause type I mentioned right at the top, but with and instead.

Can we do it with or, a disjunction? Well, yes we can, but it comes out as a warning or threat rather than a deal or an agreement.

Don't bother the tigers, or they'll attack you. 

Now, we still have to obey the instruction but if we don't, then the second part will be true: a punishment, rather than a reward for our obedience.

We can even do it with neither at all, just so long as it is a proper threat and not just a warning:

Touch my stuff, I'll beat you up. 

Now the instruction is an elliptical conditional. There's probably an understood 'If you' at the beginning, or else the link between the parts is the same as with and: if the first part is 'obeyed' (the person does carry out the action), then the second part is true.

If you could read this blog post

Sometimes, a request is expressed like this:

I'm snowed under, so if you can just book that room for me. Thanks! 

My colleague/friend/fellow twitterlinguist Damien Hall (@EvrydayLg) says that this has an implied 'that'd be good' after the if-clause. I think he's right about this, and the full form would be this:

If you can just book that room for me, that'd be good.

The if-clause is a conditional, and conditionals have to be subordinate to a main clause. So technically, this is a fragment: it's a subordinate clause set adrift, with no main clause to modify the meaning of. But we see it a lot. I do it myself, because it's a very convenient way of making a request in writing.

Written requests have become a problem, if they are from one person to another on the same level. You have to be polite and grateful, and one by one, our ways of doing it have become too abrupt. A plain request would be Please book that room for me. This is way too imperative, so we have questions. Can you book that room for me? is not technically a request: it's a question, and the askee could say I'm sorry, I'm not able to without having to say I won't. But then we feel we need to add please, and then could seems to sound more polite, and we get Could you please book that room, and then we add hedges like just as in the first example... and so on. Eventually you sit at your computer rephrasing it over and over but it all sounds like you're ordering the person around. Right now, to me, this 'unfinished conditional' construction seems to be non-imperative. It's a simple statement of fact: I'm not asking you to do anything, but if you were to happen to do it anyway, that'd be grand.

But here's why I love it most of all: it looks just like the way you ask a question in some other languages. We aren't really using it to ask a question in English: conditional-if is different from question-if, and they just happen to have the same form. But if it was question-if, look at this question in Polish (source):

Czy Basia ma kota?
'Does Basia have a cat?' (literally: 'If Basia has (a) cat')

Here, the same word czy that is used for if in an embedded question (as in English I wonder if Basia has a cat) is used for a main clause question and it looks really like the English unfinished conditionals.

We said that the English one is a conditional, not a question, and I think this is right. But imagine that it was a question: If you can book that room for me means Can you book that room for me? and we have what is apparently exactly the same syntax as Polish. (I'm not claiming it is the same - just noting the parallel.)