The indirect rein — also called the bearing rein, neck rein, or rein of opposition — acts on the horse differently from the direct rein in both its physical application and its effect. Where the direct rein leads the horse's head and nose in the direction of movement like opening a door, the indirect rein applies pressure against the horse's neck or in a direction that crosses the midline of the horse, asking the horse to move its weight or its body away from the pressure rather than following the direction of the rein.
In its simplest Western form, the neck rein is applied by moving both reins to one side — the outside rein contacts the horse's neck and the horse moves away from that contact in the opposite direction. The horse has been trained to associate neck pressure on the left with moving right, and neck pressure on the right with moving left. This frees the rider's hands from having to steer through direct mouth contact and allows the reins to be held in one hand, which is the traditional Western riding position.
In classical English riding, indirect reins — particularly the rein of opposition behind the withers and the counter rein of opposition in front of the withers — are used to shift the horse's weight, influence the hindquarters, and create collection effects that direct reins cannot produce. These applications are significantly more subtle and complex than the simple neck rein and require a high degree of feel and timing to use correctly.
The key practical distinction for most riders is that the direct rein primarily influences the horse's nose and forehand direction while the indirect rein primarily influences the horse's shoulder, barrel, and weight distribution. Together, these two types of rein aid provide the complete communication vocabulary for directing the horse's body in any direction.