This might be an old post, but that article was actually really helpful :P
Someone told me really recently that when a horse was fully on the bit his forelock and withers would be aligned horizontally, but now I'm assuming that that's wrong..
I'm glad to hear that the article was/is helpful! The entire website is a goldmine of information.
Yeah, I'm not even able to visualize what horizontally aligned withers and forelock would look like, to be honest... unless you mean that the poll is at the same height at the withers? A horse can be on the bit with the poll even with the withers, but GP dressage horses are on the bit with their polls decidedly higher than the withers in most cases.
At any rate, looking at the front of the horse alone won't determine whether he's properly on the bit/on the aids or not. Yes, a horse that is on the aids will have a certain head carriage, but a horse who is evading the bit can look similar if that's the only part of the picture. Properly on the aids, the back will be lifting and rounding (you won't see a downward angle from the hips to the cantle of the saddle), the hindquarters will be engaged and the hind legs tracking up, etc.
Where collection in the dressage sense comes into the picture, as I understand it, is when the horse begins to distribute his weight evenly across all four legs. As the hind legs begin to bear more weight, the joints compress and everything gets shorter in length and longer in height. The length from tail to muzzle shortens as the back lifts and rounds and the pelvis tucks in, and the length from ground to poll increases as the shoulders elevate slightly. The movement of the legs changes similarly with different degrees of collection - as the horse advances into higher degrees, the distance covered per step shortens, but the legs (all four of them
) remain active, coming higher in the execution of each stride.
Another wonderfully informative and helpful article on dressage-sense collection from an equally wonderful and informative website. ::: Sustainable Dressage - Collection & Its Evasions - True Collection - What It Is and How to Achieve It :::