As with everything in life there is a negative and a positive and both have to exist to have balance. When training horses there has to be a balance of reinforcement to be successful. Positive reinforcement and negative reinforcement. If I lost you at negative reinforcement, hang in there for a second.
Let us first discuss what a positive reinforcement is in horse training. A positive reinforcement is when the rider applies pressure and then releases pressure, then rewards. This could be a simple as reaching forward with the inside rein and giving the neck a pat, or it can be as big as ending the ride right when it is going very well and rubbing on the neck after dismounting. It could mean reaching forward and giving the horse some sugar. This is reinforcement of an aid by the action of the rider.
Now, for where I lost you. Let us discuss a negative reinforcement. This is not what you might think. An example of a negative reinforcement is when rider applies pressure, and the horse releases the pressure by giving. A deeper example would be when a horse bears into the bit and rushes forward. In this scenario the rider would then allow the pelvis to be pulled into the saddle as if the reins were connected to the hips and not the hands. The horse feels this pressure in the pelvis and begins to comeback to the rider, thus lightening the load in the saddle and the bridle. This is reinforcement of an aid by the action of the horse.
Both positive and negative reinforcement must be present to create a horse that fully understands the rider. When both are used, the horse learns to think and feel through the aids. It can trust the aids. The horse knows that the rider can release, but it also knows that he/she can release pressure as well. This is an immensely powerful tool to give the horse confidence and self-reliance.
Trust and understanding are built through repetition and well-rounded training. By incorporating both reinforcements into your training, you are ensuring a bond between horse and rider. You are ensuring trust and confidence.