Aristotle mentions coercion first in his description of the elements of involuntariness: “What sort of acts, then, should be called compulsory? We answer that without qualification actions are so when the cause is in the external circumstances and the agent contributes nothing.” This statement clearly marks the essence of coercion as exteriority, as opposition not only to the higher degree of interiority, of “from-withinness,” which distinguishes voluntary actions, but also to the spontaneity common to all natural processes. Aristotle gives some instances of physical coercion: a man blown from his path by the wind, and a man carried away by kidnappers.
But we know that psychical forces can also bring about coercion. For example, the movements commanded of a person in deep hypnosis have their origin externally to him in the will of the hypnotist; the hypnotized person contributes nothing by way of voluntary decision to those movements. He is an instrument moved by the external, psychical force of the hypnotist's will; that is, he is subject to psychical coercion.