Before I get into some distinctions, let me just start by reminding you that I'm German. And if you've ever ridden with a German trainer, you've probably heard something like "Diagonale und zulegen!!!" oder "Jetzt mal so richtig Zuch' drauf kriegen!" - in other words, forward, forward, forward. The idea is of course that the horse will come over his back and reach for the contact by producing the proper RPMs behind. And obviously, forward is good. But what exactly is forward? And how forward is forward? Those are fair questions given that even in the piaffe, a movement in place, and the rein back, we are reminded to think forward.
Needless to say, I get happy when a horse responds swiftly to my driving aids. This was the case also this morning in the warmup for my lesson. Yay me. Until, that was, my trainer told me to come back a notch from going *too* forward, giving me the "oh, I must recalibrate my feeling for what's a good pace on this horse"-moment.
But back to forward. Let's first exclude two things that are obviously not the kind of forward that's productive: A horse that is "behind the leg" and a horse that's "running". Behind the leg is quite easy to spot as the rider will be exerting much more energy each stride than the horse. A "running horse" horse on the other hand is taking quick steps and is not engaging the back, it might well feel like you're being run away with.
So clearly we are talking about energy and not speed; energy that is created by the hind legs flowing through the back and neck into the rein contact and from there back to the hind end. And clearly we must also be talking about balance, with the inside hind reaching under actively. That includes the "in front of the leg"-forward or working pace and the medium/extended pace-forward, but also the proper energy in the collected paces. It also includes a degree of relaxation, which sits there on the bottom of the training scale, inciting occasional arguments on whether it or rhythm should really be the first step. But combined, they get at the forward that's desirable. Because the issue with my happy forward this morning was that is caused just enough tension for the horse to brace a bit, something that I was going to address through flexion and bend within that forward, but that was better addressed by coming back to the relaxation first.
One other thing that you're also being taught by those German trainers is to never drive more with the leg than you can contain without pulling on the reins. Which means that your horse must stay in balance, on your seat, and particularly your inside leg for that to work. But that doesn't get as much attention as the demand for forward. This idea of deliberate forwardness however, gives the rider additional tools to address sticky issues by not taking them head on, but rather weaving in and out of them, giving the horse a chance to figure it out too.
P.S. Then I looked at a recent video of my riding that I quite admired a couple of weeks ago, and lo and behold, I felt that this too was a bit too quick. So today I acquired another nuance to my sense for balance and forward. Another unexpected gift.