There's a lot of talk about aids and cues in the horse world and a lot of it just confuses people. One trainer talks about using your legs as aids and another one tells you to cue your horse with your leg. Neither one probably knows what he's talking about. So it's no wonder horses get confused.
Horses don't care what a trainer calls the things he or she does, they just need to understand them in a horse logical way. As a training method, heeding uses methodically applied directional pressures to create shapes. Pressures that create shapes are called aids. Once the horse understands what shape you want when you apply a particular pressure, you can associate a cue or signal with that shape. So now you can use that cue to tell the horse exactly when you want him to give you the shape. You teach with aids. You ask with cues.
Notice what goes into an aid. It's a pressure. It's applied so it indicates the direction you want the horse to go. And it is applied methodically and consistently. That's not the same as forcefully or insistently or repeatedly. A lot of people use swear pressures instead of aids. Instead of touching the horse with a whip or even just pointing it at him the right way, they slap him with it. Loud swear pressures get a reaction from the horse but they don't teach shapes.
Aids are horse logical. The horse reacts to that pressure or aid in a predictable way that is just natural or instinctive for a horse. For example, if you start approaching a horse from behind, he will turn his head one way or the other to see what's coming. If you're a little to his left, he'll turn his head to the left so he can watch you coming. If you're a little to his right, he'll turn his head to his right.
If you're coming too fast or he's a spooky kind of horse, he may move off and ask questions later. If it's open in front of him, that's the direction he'll go. If it's not, he'll turn in whatever direction he feels he has an opening. Once he's far enough away to feel safe from what might be a predator, he'll turn to take a good look and figure out what's coming. (TRUE? IS THIS CORRECT HORSE LOGIC?) Those are horse logical responses to the pressure you put on the horse as you approached him from behind.
Cues are conditioned responses that are not necessarily horse logical. Cues are supported by rewards. You use a pressure to create the shape you want. You give the horse the cue as soon as he creates the shape. Then you reward him with scratching or something else he likes to tell him that was what you wanted. Eventually you can stop using the aid because as soon as the horse gets the cue, he gives you the shape and looks for his reward.
Once the horse understands that a particular cue indicates a shape you want, you don't need to use the aid to get that shape. Conditioning the horse to respond to cues instead of just to aids is kind of like putting an automatic transmission on a sports car. Now anyone can drive it. A cue is something a trainer can sell with the horse. The owner can ride it and cue it and doesn't have to understand all this stuff about aids to get the shapes he wants to play people games on horseback.
What happens when you stop supporting the cue with a reward? The horse will start backing down the learning curve. First he learned the cue meant he got a reward for giving you a shape. Now he gives you the shape when he gets the cue but there's no reward. Pretty soon he stops giving you the shape when he gets the cue because there's nothing in it for him and there's no horse logical reason to create that shape.
When you put cues on a horse, you've got to monitor the horse's response to those cues. When the horse starts to ignore the cue, you need to drop back to the aid that was used to teach the shape you wanted in the first place and remind him of the relationship between the cue and the shape. Retraining horses to respond to cues is what helps keep trainers in business.
So you need to understand both aids and cues and understand which ones you're using to ask the horse to play our people games. If the horse responds to cues and he starts forgetting those cues or missing them, you need to understand the aid that created the shape in the first place and go back to it to retrain the horse. And use horse logical aids, not swear pressures.