Peice of text can explain so much.
Was written by the Grand Prix Rider - Kyra Kyrklund
" Half halt is like the rubbish of riding - you put all the difficult things in there, and call it half halt. The half halt is not something you learn, it comes from being able to controll the frame of the horse. "
Its quiet simple really. I agree 100% with her.
Controll the frame - and use controll the leg, use you're whip as a longer hand to connect the horse. Make him move more behind make him bend correctly the more he develops the ability to collect. The more collection develops, the more the horse has to being his legs under him.
Why do we ask the horse to do more track work?
Well its quiet simple really..to get his legs under him and to get him listening to the aids..To move on two tracks the has to be listening to the rider's leg..and you can teach that with the leg yeild. Some horse rider's think that it is best to rush the leg yeild (as I've herd) I don't believe it tho..half pass comes from listening to the aids.
I hope that cover's anything you where wanting to know.