The 4 natural aids are our means of transmitting information to the horse for lines-of-travel, gaits, shaping, displacing, and adjusting/rating.
These aids are: the VOICE; the SEAT and its’ WEIGHT; the LEG; and the HAND.
The natural aids are NOT vague guidelines. They are DEFINITE and PRECISE. They do not vary. These must be made uniform and deliberate because they form a language that is for all horses. If you're not training the Natural Aids verbatim, there's nothing natural about your riding.
In a well-trained, a finished horse, these 4 Natural Aids form a literal language: Equitation. This language is delivered by a rider whose position is plumb, matched on each side, and elastic.
Training is teaching this equitation language by the Law of Association of Sensations and calibrating the rider’s 4 Natural Aids, which are the CAUSE to the horse’s understanding response, which is the EFFECT.
Don't be illiterate! Study, practice, and master the 4 Natural Aids.