What is Equus and how does Monty Roberts use it?

Equus is Monty Roberts's term for the body language communication system of horses — the specific vocabulary of postures, movements, and signals through which horses communicate with each other and that Roberts believes humans can learn to use in their interactions with horses. Roberts adopted the term to give his method a vocabulary that distinguished the horse's communication system as a genuine language rather than simply instinctive behavior — Equus, from the Latin for horse, became his name for the system of signs that horses use to establish social relationships, communicate safety and threat assessments, and negotiate their positions within the herd hierarchy. Roberts's use of the term reflects his conviction that understanding and using Equus — the horse's own communication language — is what makes join-up and his broader approach to horsemanship effective. When he drives a horse away in the round pen using squared-up body posture and direct eye contact, he is speaking Equus in the threat dialect; when he drops his energy, turns sideways, and avoids eye contact to invite the horse to approach, he is speaking Equus in the invitation dialect. The concept of Equus has been both widely adopted — it provides useful vocabulary for thinking about the horse's communication system — and critiqued by equine behavioral scientists who note that Roberts's specific interpretation of horse body language does not always align with the scientific understanding of equine communication, though the general principle that horses communicate through body language that humans can learn to read and use is well supported by behavioral research.