A student asked me to read this article by Jim Wofford, http://equisearch.com/horses_riding_training/english/eventing/wofford_eventing_lives_051408/index.aspx .
My thoughts on this very important topic follow.
I think Jimmy is entirely right, but I want to clarify what is meant by collection--the difference between that and self-carriage. I spent several years riding--and teaching-- the Littaur/Chamberlain philosophy and think there is a lot to be said for that whole philosophy. For most riders, I think that is the way people should ride. I think the horse must first of all and forever be ridden in such a way that he is in balance. When he is in balance then he can become supple and in this condition be both more responsive to the rider and more athletic.
Letting the horse find his way and allowing him to make mistakes that he can learn from are critical in jumping and actually terribly important in dressage.
When a horse is in balance, he is in self-carriage, and he must learn to go in self-carriage from the earliest steps in his training all the way through to the highest levels of training, whether it be in dressage or eventing. Self-carriage is a the state where a horse can maintain his tempo without being held up by the rider. In self-carriage a horse is in balance and moving freely forward.
Dressage should be used to condition the horse to a greater level of strength and agility. When dressage becomes an end in itself, then the horse and rider (ideally) lose their personal identity and work as an harmonious unit. This kind of work begins at 4th level, not before. The unity of the two entities should be sought from the beginning, initially so the rider can lead the horse through progressively challenging exercises in order to develop the physical ability of the horse--increase his strength and increase his agility. The requirements of the training come to its peak (ideally, again) in the Grand Prix when the horse is able to extend and compress very easily, remain lively, responsive (because of the balance thing) and eager.
At the beginning of training the horse is presented with various challenges and should be asked to participate in answering these challenges because when he does, he has become a willing partner in the relationship.
Defensiveness (non suppleness) can only cause a horse to be more dependent, not less dependent on you.
I don't think that the aids are anything that a horse should have to "learn." The rider needs to ride in such a balance that she can trigger certain expected responses from the horse, responses that are no more complex than blinking the eye when something gets into it. I can get on any horse from any background and if he has not had his natural responses trained out of him--so he doesn't allow his body to respond (over-rides his reflexes)--I can do whatever the horse is capable of. I can't make a training level horse do a canter pirouette because he is not strong enough to do so. It isn't that he doesn't "understand;" it's simply because his body isn't there yet. I can't do the splits. I don't have to learn how to do the splits; I have to condition myself to that level of ability.
The more a horse has to figure out what we are "teaching" him, the more anxious he becomes. A horse should not have to figure anything out in dressage--a horse is not designed to "figure things out." A horse is a reactive creature and he should be guided to react in a way that is favorable to the training (in dressage.) A horse should be allowed to respond as his body reacts naturally to the rider's aids. (Initially, of course, he must learn that the legs of the rider are more than a mere annoyance on his sides, but other than that the dressage aids are designed to trigger natural responses of the horse--and we do have to heighten that response with a flick of the whip--and the horse responds to the sting as he does to a fly, by lifting a leg--or as amplified by the spur, and sometimes the response needs to be more than a little encouraged by the rider as some horses perfer to lie in bed all day and not have to do much of anything.)
I think that horses who anticipate in dressage are horses who are being "taught" rather than being conditioned. These horses worry that they might do the "wrong" thing and anticipate what the rider wants, using a little mental strategey to save them punishment. A horse has very limited powers of reasoning and when asked to perform and use these limited powers, they become anxious and anticipate rather than relaxing into their body's natural ways of doing things.
When a rider is inaccurate with the aids, the horse must learn to over-ride his physical responses to the aid. For instance, if the rider doesn't sit on the left seatbone to turn to the left, the horse has then the task to learn "turn left means to go right." Pretty hard. Horses are pretty wonderful and do learn to compensate, but when they must compensate they are not so fluid because they have to hold their bodies against their natural responses and often have to "learn" what is being expected of them. An example I often use to explain this is for us to think of having our own reflexes tested by a doctor. The doctor should tap us right under our knee for this test. If, instead, the doctor tapped us in the middle of our shins and then punished us when we didn't respond, we would become more and more "defensive," muscles tensing up, worry developing. At some point we would kick our leg when the doctor taps our shin, and then the doctor would pat us and tell us how "good" we had been. Then we would be frantic to try to put together the "good"--the effect--with the cause--what did we do to get the "good."
The problem in training is figuring out whether a horse is resisting leaving their comfort zone because of pain or the remembrance of pain. I was very lucky to have worked with a sports medicine vet for 22 years. He helped me with every horse that I trained, helped me answer whether the horse had an actual physical problem or simply needed to be pressed into "raising the bar." As a trainer, I was often pressed to take the horse to a level faster than was comfortable for the horse, but while I had to do that, I was able to do it humanely. I have to say that in the 25 years of training horses for the show ring, I never had a horse go lame from the training, and as a judge recently told me, "Your horses always looked so happy."
I think the horse should participate in the training. He needs to be guided; he needs to be conditioned; he needs to be improved physically; he needs to have confidence in the rider and she in him. Riders in the lower levels of eventing are far away from the collection that Jimmy is talking about in his article. Let go of your horse, and learn how to put him in a position so that he can become more supple so that he can become overall more elastic and stronger.
In jumping, the horse has a lot of decisions to make and he must be allowed to do so, must have the confidence to be able to do so. Horses that jump in competition know about jumping. Deer know about jumping. Horses in competition have the terraine, the rider's balance, and the turns and combinations to deal with. I believe that a horse, whether negotiating a jumping course or a dressage test, must be put into a position of being able to do what is being required of him and then allowed to do it. The best we can do for him is train him so he is physically able to respond to the test--either jumping or dressage--put him in a position to perform and then allow him to do it by staying with him and not throwing him away.
A horse should become a dancing partner not a servant. The rider must allow the horse to mature and take responsibility in the dance or this will severely limit his capabilities to grow. Otherwise the horse is limited to the rider's control and direction and can gain no confidence in his own ability to negotiate the obstacles.