I don't know about you, but I don't like it when people are rude.
Politeness is generally very important,
especially if you want people to help you with something.
If you want someone to do something for you, there are different ways of
expressing it in English, depending on how polite you want to be.
If I say:
"Open the window!"
it's quite direct, isn't it?
It's the imperative form, which is more or less an order.
"Open the window, please!"
Adding the word 'please' does make it more polite,
but it's still quite direct.
"Can you open the window, please?"
Now we are getting more polite, but why is this more polite?
Well, one reason is because this is now a question.
So it's more of a request than an order.
And because it's a question, it's easier to say no.
Let's now use could instead of can.
"Could you open the window, please?"
Could is more polite than can
and this is where it begins to get interesting.
Why is:
'Could you open the window, please?'
more polite than:
'Can you open the window, please?'
Well, it's all to do with the relationship
between can and could and the idea of distance, of remoteness.
'Could' can be described as the remote form of 'can'.
Sometimes that distance is time.
"I can swim."
That's an ability I have now.
"I could swim when I was four."
That's an ability I had at a time in the past.
Sometimes that distance is between what is real and what is imagined.
"I can't do that in my head."
This is something that is not possible for me to do now.
"I couldn't do that even if I had a calculator."
This is something that's not possible for me to do,
even in an imagined situation where I have a calculator.
And sometimes distance is in relationship.
"Can you open the window, please?"
"Could you open the window, please?"
Could puts more social distance between speaker and listener.
That makes it more polite as it's less uncomfortable for someone to say no.
Now, we're not talking about actual distance here.
We're not saying you have to be physically further away to be polite,
but it is a good way to visualise it. The further the speaker is away,
the easier it is to say no and 'could' puts you further away.
Open the window!
Open the window, please!
Can you open the window, please?
Could you open the window, please?
And in English, we can make that distance even further too
using past forms and modal structures.
I was wondering if you wouldn't mind opening the window
if it's not too much trouble.
For a simple request like opening a window,
that one is probably a bit over the top.
One very important thing to remember, perhaps more important
than the words themselves, is the way they are spoken.
It's only polite if the tone of voice is polite.
You can make a polite form of words less polite
if you stress it in a different way. For example:
"Can you open the window?"
"Could you please open the window?"
So sounding polite is a combination of words and the way you say them
and when it comes to words,
'could you' is more polite than 'can you'
and longer phrases with past forms and modals are more polite still.