How does the half-halt improve contact and connection in dressage?

The half-halt improves contact and connection because it addresses the root physical cause of most contact problems — the horse's tendency to fall onto its forehand and use the contact for balance rather than maintaining its own self-carriage — by momentarily asking the hindquarters to carry more weight and the horse to rebalance. When a horse leans on the contact, the physical reason is almost always that more weight is on the forehand than the hindquarters can comfortably support without the rein's assistance, which is a balance problem rather than a contact problem. The half-halt addresses this balance problem directly: by momentarily engaging the horse's core and hindquarters through the seat and back before allowing the energy to flow forward again, it shifts weight from the forehand to the hindquarters and allows the contact to lighten because the horse no longer needs the rein for support. Repeated correctly timed half-halts gradually develop the horse's ability to maintain this better balance between applications, with each successful half-halt building the physical capacity for self-carriage that eventually allows the horse to maintain good contact without constant intervention. The half-halt also improves connection — the flow of energy and communication through the horse's body — because it activates the hindquarters and requires the energy generated there to flow through the horse's back and out through the contact rather than dissipating in forward movement or resistance. A horse that accepts the half-halt and responds to it by lifting its back and lightening the forehand is showing both that it is genuinely through — the half-halt could not reach the hindquarters if the horse were blocked anywhere — and that the contact is genuine communication rather than mere rein pressure.