How is it that you can detect a change of key in a piece of music you've never heard before, even if you're not particularly adept at reading music?
Music is just one note after another, isn't it, in theory, so how does the ear pick up that a note doesn't 'go' with the previous one and is starting a 'new grouping'?

Usually it's because the arrangement prepares your ear for the key change in the sequence of chords that precedes it. Typical chords leading into a key change are the 7th or suspended 4th chord of the fifth note in the new key, or a change from the major chord to minor chord in the fourth note of the old key. Concretely, if the old key is C and the new key is D for example, you'd get an A7 or Asus4 (or even an A7sus4!) instead of whatever chord you were expecting. If the old key is A and the new one is C, you might get a D major (expected), then a D minor (unexpected), then a G, by which time your ear is now expecting a C.
Other times the whole melody and accompaniment will change without warning, but the change is so wholesale there's no real confusion about what key you're in.
On the other hand if you have someone singing a capella who suddenly changes key without any preparation sequence, you will indeed be confused for a while before realising it's because there's a new key going on.

Hope this helps.

What he said.

We're all in agreement then

Yes, it helps.
But what I mean is, when you say, 'your ear is expecting...(whatever chord)' that's a bit fascinating, isn't it? In the sense that it must be innate

Well, how shall I put this, Dibble. If something is innate, its form is there in your brain from birth, not something you've acquired through tuition or experience.
An example would be your knowledge of the inner workings of HUFC

it's like knowing the way to the kebab shop innit?

Well yes and no; it's more a case of what we're used to than one of being being innate. The whole of western music is built around a concept called the circle of fifths, and what I described is part of that concept. This goes unnoticed by most people because they don't need to know it's going on. But it's really no more than a simple mathematical progression, and following mathematical progressions is pretty much innate.
The chord change is like watching 1,2,3,4 repeat itself over and over, so you're always expecting a 4 to follow the 3, until suddenly you get a 5 or 7 or whatever instead of the 3 so you're alerted to a change.

Do you mind, elvis? I have extremely musical lugs

But that's what I mean , Richard, maths is innate

If by "maths" you mean "pattern recognition" I agree.

What I find a bit spooky is the way the workings of the brain mirror things in the external world.
Over the centuries, how many phemomena have been found to correspond to calculations that physicists once made in their heads, with no reference to anything outside

Isn't it amazing how these things are inter connected.
Our lass uses 'pattern recognition' when she's knitting, and 'maths' when she counts the rows.
She doesn't do it whilst sat at the old joanna though.

Maybe if we said, "Dibbs, understanding is not innate in you," you'd understand.

Well, you know when you move house and you don't quite trust the old occupants...

or alternatively

Key changes are something the Clash never bothered with so it won't really matter to you