When you are with your horse it is important to be consistent. Just like us, horses are more comfortable when they know what to expect from people. There are those people whose behaviour is erratic. You never know if they will greet you like a long lost friend or if they will ignore you completely. Usually when I encounter one of those people it makes me uncomfortable and apprehensive. It is the same with horses.
Horses are only comfortable with you when they are confident in whom and what you are and how you are going to behave around them. When you are with horses your demeanour should be calm, patient and confident. If you consistently demonstrate this behaviour the trust your horse has in you will grow.
Body language, your expression and actions, is the primary means of communicating with your horse. Most people won`t respond well if you speak to them in English, then switch to German, French`, Italian and then back to English. Its the same with horses. For productive, successful communication with your horse your body language must be consistent. This is something that nearly all clinicians agree on. If you expect a horse to respond to a cue you need to make sure you are giving the cue consistently and you must be consistent in your expectations of the horses response.
Clinicians each have their own methods, techniques and tools which they use, but all are ased on the same fundamentals of horse behaviour. There is nothing wrong with mixing the methods, techniques and tools as long as you are consistent in the way that you use them. People and horses are unique individuals. Build the language that works best for you and your partner and be consistent in using it. When you learn a new word(cue) your horse must learn it as well. The cue must mean the same thing to both of you every time it is used.
Horses do learn to respond to vocal cues. It is important that these cues be very consistent. In my experience they need to be taught together with physical cues. For example when I teach my horse to back up I will point at my horses chest, I will look at one of his front feet and I will say BACK. When he moves the foot back I will stop all cues. With the vocal cue it must be give the same way every time, the same tone volume and exactly the same word. Remember it is the sound the horse learns not the meaning of the word BACK. Once learned the horse will respond to any of the cues when they are used separately. I keep vocal cues to a minimum because it is not the most natural cue for horses.
Consistency is one of the pillars of your foundation training. As your knowledge and abilities are developed with practice, your consistency will improve, if you pay careful attention to what you are doing and how you are doing it.