(” Not according to the FEI, however, . . “)

There is nothing like a good philosophical argument, especially one boiling with indignation and angst and carried on between parties with little in common who insist on talking past each other. A recent one I encountered on Facebook and proposed by Lesley Stevenson was this: Can lateral movements only be done “on the aids” or can they be used to help put horses on the aids?

There is a semantic component to this controversy (which we’ll get to later) but beyond that the answer depends on the knowledge level of the rider and her goals.
Yes, the movements will only produce their originally intended result if the horse is on the aids and through. For instance, the rule book states a major reason to ride shoulder in is to enhance the engagement and collection. If your horse is not on the aids, that simply will not happen!

HOWEVER, there are other reasons to do lateral work even if a horse is not completely on the aids or even round.

Experienced riders have many tools in their kit. And they have a very good awareness of how much their horse is listening and responding to each of their aids. That they can put any part of the horse anywhere they want and keep him connected is a given. When they can’t, they sense it immediately and rectify the situation.

A less experienced rider not only lacks this kind of control, but is often unaware of what she cannot do, being unable to hear what the horse is trying to tell her.
So where does such a rider gain those tools – the physical ones and the awarenesses? Fortunately (and not coincidentally) many of the mechanical coordinations that are required to produce recognizable lateral movements are the same coordinations that riders must learn to put their horse on the aids. Riding structured yielding exercises which involve the pushing and receiving/allowing/non-allowing aids – the “verbs” and the modifiers – gives your student a lab in which to figure out how to combine them plus immediate feedback from the horse
as they work. Roundness, displacement, and softening are empirical proof of being on the right track. Learning to do the movements can really give the rider the tools to solve much more complex problems.

Getting back to the semantic part of the argument, the rule book is quite specific about what the FEI and the USEF define as a “lateral movement.” In common parlance leg yielding and turns on the forehand are referred to as such because, well, they are movements which appear to be directed laterally. Not according to the FEI, however, which offers a very short list of lateral movements – shoulder-in, travers, renvers, and half pass. Regardless of how inclusive the category is, its members have two functions. They teach the rider how to operate the tools, and then use them to gymnasticize the horse.