Why does the announcement at London Underground stations say 'The lift on the left shall (rather than 'will' ) be the next lift' and why does it sound weird?
I've always been interested in phonics, the way in which the meaning of a word is affected by its sound. I've written before now on the subject of why so many action heroes have the initials JB - James Bond, Jason Bourne, Jack Bauer. I reckon it's because of the sound of the consonants - the J promises adventure, as in jump, jaunt, journey and the parachutist's cry of 'Geronimo!', while the plosive B is comforting, suggesting a happy ending.
By contrast, heroes with the initials JC tend (despite the religious connotation) to be more morally ambiguous, the harsh C sound denying reassurance - Jack Carter, Jerry Cornelius, John Constantine. (If you wanted to get really clever, you could argue that the two best actors to play James Bond brought something of that harshness through the C sounds in their own surnames.)
Back to that 'shall'. Standard usage guides are fairly clear on this; the rule is that, when using the future tense, 'shall' denotes simple futurity, 'will' is for intention, determination and, in its other sense, will. To this extent the underground announcement is by-the-book.
However, a little thought demonstrates that everyday usage is exactly the other way round, and has been for many years. 'I will get up early tomorrow' is a statement of fact; 'I shall... ' is a resolution. General Douglas MacArthur's 'I shall return!' sounds ludicrous as 'I will...' It works the same way with negatives - recalcitrant toddlers shout 'Shan't!' rather than 'Won't!'.
Why did the two words change places? Again, I think it's in the consonants. W is weak, watery, and wimpish - one of the reasons why a German accent still seems sinister to English ears is its lack of that sounds - 'Ve heff vays...'. Sh, by contrast, is effortful - you have to shove, shift, or schlep it, and it can be a bit shitty. 'Shall' took over from 'will' to indicate determination simply because the word sounds more like what it describes.
That's why the underground announcement sounds odd - it sounds like it's making a resolution rather than simply promising a lift. The etymology says that 'shall' is correct, but phonetics guarantees, in this context, the triumph of the 'will'.