  Although one could start earlier, Aquinas offers a picture of what might be regarded as the traditional, canonical understanding of coercion, its importance, and consequences. Discussion of coercion (sometimes also described as “compulsion”) recurs in the Summa Theologica under several headings. In a discussion of necessity and the will, he notes that when we speak of necessity, we mean “that which must be” (Aquinas, ST, I.II Q6 A6). There are various ways something may be necessary. Coercion, he says, is a kind of necessity in which the activities of one agent — the coercer — make something necessary for another agent.  The “necessity of coercion” is that in which “a thing must be, when someone is forced by some agent, so that he is not able to do the contrary” (ibid.). Such necessity is “altogether repugnant to the will,” (ibid.) meaning that what is done because of coercion is not done voluntarily.  To say that something is voluntary, for Aquinas, implies that it follows from or is in accord with one's inclinations; in contrast, coercion is linked with the notions of violence and the involuntary.