What is Martin Black's view on the progression from snaffle to bridle horse?

Martin Black's view on the progression from snaffle to bridle horse carries forward Bill Dorrance's understanding of the vaquero tradition's complete developmental arc, treating the full progression not as a historical curiosity but as the most complete expression of what patient, feel-based horsemanship can develop in a horse and a rider. The snaffle phase, in Black's teaching, is not merely the beginning stage to be moved through efficiently but the period in which the foundational qualities of lightness, suppleness, and genuine responsiveness to feel are developed to the depth that subsequent stages require. A horse moved into the hackamore before these qualities are genuinely established in the snaffle will carry gaps in its training that the hackamore's different communication style makes harder to address rather than automatically filling. The hackamore phase develops the horse's response to nose and chin pressure — a different physical application of the same feel-based communication principles — and the transition to the two-rein, in which the horse is ridden simultaneously in the hackamore and in a bridle, allows the horse to develop its understanding of the spade bit's communication while still having the familiar hackamore as a reference point. The finished bridle horse — working in the spade bit with the lightest possible contact, responding to the weight and position of the reins rather than to direct physical pressure — is for Black the expression of what the full development of horse and rider through the vaquero progression achieves. His concern is not with the equipment itself but with what the equipment reveals about the quality of the training at each stage — a horse that is not genuinely light and responsive in the snaffle before the progression continues is a horse whose training has been rushed past its genuine development.