First, let's take a look at some official definitions:
SHW330.3 The lope is an easy, rhythmical three-beat gait. Horses moving to the left should lope on the left lead. Horses moving to the right should lope on the right lead. Horses traveling at a four-beat gait are not considered to be performing at a proper lope. The horse should lope with a natural stride and appear relaxed and smooth. It should be ridden at a speed that is a natural way of going. The head should be carried at an angle which is natural and suitable to the horse’s conformation at all gaits. (pg. 114)
USEF Rulebook, Morgan Division
13. Canter: Smooth, collected and straight on both leads.
14. Lope: Smooth, slow, straight and a three beat cadence.
15. Extended Lope: A lengthening of stride while maintaining a smooth, straight, three beat cadence.
16. Extended Canter: The extended canter should be ground covering, free moving and smooth. The extended canter should show a definite lengthening of stride, while still being controlled and mannerly. Extreme speed SHALL be penalized.
17. Hand Gallop: Long, free ground covering stride under control. Not a fast collected canter, but a true lengthening of stride, correct and straight on both leads. Extreme speed penalized.
Note: number of beats is only specified for lope. Within the chart for "major and minor" faults in the Morgan Western Pleasure division (pg. 951), number of beats is not listed. Thus, it is up to the discretion of the judge whether it should be considered a major or minor fault. The Arabian Western Pleasure division does specify "not performing a three beat lope" as a major fault (pg. 345). The Arabian division, in general, has stricter and more cut & dry rules. The Morgan Park Saddle section uses "proper cadence" as one of its criteria, but never mentions number of beats (pg. 944).
USEF Rulebook, Dressage Division
1. The canter is a three-beat gait where, in canter to the right, for example, the footfall is as follows: left hind, left diagonal (simultaneously left fore and right hind), right fore, followed by a moment of suspension with all four feet in the air before the next stride begins.
4. The following canters are recognized: Working canter, lengthening of strides, Collected canter, Medium canter and Extended canter.
a. Working canter. This is a pace between the collected and the medium canter, in which a horse’s training is not yet developed enough and ready for collected movements. The horse shows natural balance while remaining “on the bit”, and goes forward with even, light and active strides and good hock action. The expression “good hock action” underlines the importance of an impulsion originating from the activity of the hindquarters.
b. Lengthening of strides. In some tests, “lengthening of strides” is required. This is a variation between the working and medium canter in which a horse’s training is not developed enough for medium canter.
c. Collected canter. The horse, remaining “on the bit”, moves forward with the neck raised and arched. The hocks, being well-engaged, maintain an energetic impulsion, enabling the shoulders to move with greater mobility thus demonstrating self carriage and an uphill tendency. The horse’s strides are shorter than in the other canters, without losing elasticity and cadence.
d. Medium canter. This is a pace between the working and the extended canter. Without hurrying, the horse goes forward with clearly lengthened strides and impulsion from the hindquarters. The rider allows the horse to carry the head a little more in front of the vertical than in the collected and working canter, and at the same time allows the horse, to lower the head and neck slightly. The strides should be balanced and unconstrained.
e. Extended canter. The horse covers as much ground as possible. Without hurrying, the strides are lengthened to the utmost. The horse remains calm, light and straight as a result of great impulsion from the hindquarters. The rider allows the horse to lengthen the frame with a controlled poll and to gain ground. The whole movement should be well-balanced and the transition to collected canter should be smoothly executed by taking more weight on the hindquarters.
In all of these very different competitions, a four-beat canter or lope is considered a flaw. So what is the difference between them? Are good canters and lopes always three-beat? Problematically, no.
The most visible, and visibly problematic, of the four-beat canters and lopes are in Western divisions, especially among stock horse breeds. AQHA specified four-beat lopes as a flaw after USEF did, and Quarter Horses are often easier to train to perform a four-beat lope than other breeds. There is still some disagreement among judges in all breeds about if it is a flaw and how severe a flaw it is. There are related discussions on headcarriage, as often an extreme four-beat lope also has a very down hill appearance, with the horse leaning on the forehand and the head carried below the chest. This sort of movement that is very recognizable, and while it does cause the horse to cover a minimum of ground (i.e., go slow), it is clearly detrimental to the horse. I won't show examples here, but if you search youtube for "western pleasure" you will find a range of examples. While seeing the break if the footfalls can sometimes be difficult without slow-motion, horses that move in this way have a noticeable hitch in their stride as they move forward using their backs and forelegs rather than their hips and hindlegs.
The second place where this type of gait is very noticeable and not uncommon is in saddleseat. It is not, however, talked about as a number of beats issue. It is most often talked about as a shoeing issue, as the heavy shoes and action devices can often cause the same hitching four-beat gait as western pleasure riders can achieve by backing the horse out of the bridle. In saddleseat, this gait is hugely animated, and when achieved more by equipment than by training and conditioning it can appear very strange and un-horselike. This is, of course, exemplified most by the "big lick" walking horses, but can be seen in varying degrees anywhere a collected, animated canter is desire: park classes, most other saddleseat classes, and yes, even in dressage.
But wait, didn't I say that a four-beat canter or lope isn't always bad? I did. The reason lopes often devolve into four-beat eyesores is because we humans, as rider, trainers, and judges, get stuck on the idea of "slow." We forget that the lope is actually a type of collection, and requires building up the horse's strength, stamina, and coordination. The reason saddleseat and even dressage fall prone to a similar four-beat gait, with the horse laboring more from its front end than its hind, is the same. It is a lack of conditioning. That lack can be temporary, a moment in the horse's progression, or it can become chronic if we are not aware of the issue. The problem, however, is not actually in the number of beats.
|This pirouette is lovely, balanced, strong. And four beat.|
Also this article is well worth reading.
|Neither I nor the judge placed this leggy Morgan first,|
but she does show how the park canter can be four beat
without causing an inversion of the back.
|or how about this jumper doing canter poles|
These are all cases of four-beat canters that are 'correct;' meaning, they maintain the soundness of the horse and its balance to be able to move into a different gait or maneuver. They tend to go to four beats due the the degree of collection, with the hind of the diagonal pair landing before the fore, but the pair leaving the ground together. Now go back and look at those youtube videos. Look closely at the ones you didn't like. Play with the pause button. Are any of those broken looking lopes three-beat? I'd bet a few of them are. Because of the focus on the number of beats, that issue is often fixed without addressing the underlying cause. Just as shoes aren't necessarily the issue in saddleseat (plenty of keg-shod horses also move in a disunited fashion). The canter, or even the lope, moves fast. So we have to learn to see fast, or take advantage of the technology we have that lets us see it more slowly, in more detail, and play it over and over again. We need to look at the quality of the movement, rather than the quantifiable numbers of how they move. No matter the discipline, we need to look at the whole picture.
I should also footnote this post with two other cases of (non-gaiting) fourbeat, being the true gallop (which is by definition four beats) and the break or jump, the little-discussed transition 'gait' see in racehorses, barrelhorses, ropers, and others who accelerate suddenly.